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nodejs 22.14.0%2Bdfsg-1
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            <li class="pinned-header">Node.js v22.14.0</li>
            
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        Table of contents
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      <div class="picker" tabindex="-1"><div class="toc"><ul id="toc-picker">
<li><span class="stability_2"><a href="#test-runner">Test runner</a></span>
<ul>
<li><a href="#subtests">Subtests</a></li>
<li><a href="#skipping-tests">Skipping tests</a></li>
<li><a href="#todo-tests">TODO tests</a></li>
<li><a href="#describe-and-it-aliases"><code>describe()</code> and <code>it()</code> aliases</a></li>
<li><a href="#only-tests"><code>only</code> tests</a></li>
<li><a href="#filtering-tests-by-name">Filtering tests by name</a></li>
<li><a href="#extraneous-asynchronous-activity">Extraneous asynchronous activity</a></li>
<li><span class="stability_1"><a href="#watch-mode">Watch mode</a></span></li>
<li><a href="#running-tests-from-the-command-line">Running tests from the command line</a>
<ul>
<li><a href="#test-runner-execution-model">Test runner execution model</a></li>
</ul>
</li>
<li><span class="stability_1"><a href="#collecting-code-coverage">Collecting code coverage</a></span>
<ul>
<li><a href="#coverage-reporters">Coverage reporters</a></li>
</ul>
</li>
<li><a href="#mocking">Mocking</a>
<ul>
<li><a href="#timers">Timers</a></li>
<li><a href="#dates">Dates</a></li>
</ul>
</li>
<li><a href="#snapshot-testing">Snapshot testing</a></li>
<li><a href="#test-reporters">Test reporters</a>
<ul>
<li><a href="#custom-reporters">Custom reporters</a></li>
<li><a href="#multiple-reporters">Multiple reporters</a></li>
</ul>
</li>
<li><a href="#runoptions"><code>run([options])</code></a></li>
<li><a href="#suitename-options-fn"><code>suite([name][, options][, fn])</code></a></li>
<li><a href="#suiteskipname-options-fn"><code>suite.skip([name][, options][, fn])</code></a></li>
<li><a href="#suitetodoname-options-fn"><code>suite.todo([name][, options][, fn])</code></a></li>
<li><a href="#suiteonlyname-options-fn"><code>suite.only([name][, options][, fn])</code></a></li>
<li><a href="#testname-options-fn"><code>test([name][, options][, fn])</code></a></li>
<li><a href="#testskipname-options-fn"><code>test.skip([name][, options][, fn])</code></a></li>
<li><a href="#testtodoname-options-fn"><code>test.todo([name][, options][, fn])</code></a></li>
<li><a href="#testonlyname-options-fn"><code>test.only([name][, options][, fn])</code></a></li>
<li><a href="#describename-options-fn"><code>describe([name][, options][, fn])</code></a></li>
<li><a href="#describeskipname-options-fn"><code>describe.skip([name][, options][, fn])</code></a></li>
<li><a href="#describetodoname-options-fn"><code>describe.todo([name][, options][, fn])</code></a></li>
<li><a href="#describeonlyname-options-fn"><code>describe.only([name][, options][, fn])</code></a></li>
<li><a href="#itname-options-fn"><code>it([name][, options][, fn])</code></a></li>
<li><a href="#itskipname-options-fn"><code>it.skip([name][, options][, fn])</code></a></li>
<li><a href="#ittodoname-options-fn"><code>it.todo([name][, options][, fn])</code></a></li>
<li><a href="#itonlyname-options-fn"><code>it.only([name][, options][, fn])</code></a></li>
<li><a href="#beforefn-options"><code>before([fn][, options])</code></a></li>
<li><a href="#afterfn-options"><code>after([fn][, options])</code></a></li>
<li><a href="#beforeeachfn-options"><code>beforeEach([fn][, options])</code></a></li>
<li><a href="#aftereachfn-options"><code>afterEach([fn][, options])</code></a></li>
<li><a href="#assert"><code>assert</code></a>
<ul>
<li><a href="#assertregistername-fn"><code>assert.register(name, fn)</code></a></li>
</ul>
</li>
<li><a href="#snapshot"><code>snapshot</code></a>
<ul>
<li><a href="#snapshotsetdefaultsnapshotserializersserializers"><code>snapshot.setDefaultSnapshotSerializers(serializers)</code></a></li>
<li><a href="#snapshotsetresolvesnapshotpathfn"><code>snapshot.setResolveSnapshotPath(fn)</code></a></li>
</ul>
</li>
<li><a href="#class-mockfunctioncontext">Class: <code>MockFunctionContext</code></a>
<ul>
<li><a href="#ctxcalls"><code>ctx.calls</code></a></li>
<li><a href="#ctxcallcount"><code>ctx.callCount()</code></a></li>
<li><a href="#ctxmockimplementationimplementation"><code>ctx.mockImplementation(implementation)</code></a></li>
<li><a href="#ctxmockimplementationonceimplementation-oncall"><code>ctx.mockImplementationOnce(implementation[, onCall])</code></a></li>
<li><a href="#ctxresetcalls"><code>ctx.resetCalls()</code></a></li>
<li><a href="#ctxrestore"><code>ctx.restore()</code></a></li>
</ul>
</li>
<li><span class="stability_1"><a href="#class-mockmodulecontext">Class: <code>MockModuleContext</code></a></span>
<ul>
<li><a href="#ctxrestore_1"><code>ctx.restore()</code></a></li>
</ul>
</li>
<li><a href="#class-mocktracker">Class: <code>MockTracker</code></a>
<ul>
<li><a href="#mockfnoriginal-implementation-options"><code>mock.fn([original[, implementation]][, options])</code></a></li>
<li><a href="#mockgetterobject-methodname-implementation-options"><code>mock.getter(object, methodName[, implementation][, options])</code></a></li>
<li><a href="#mockmethodobject-methodname-implementation-options"><code>mock.method(object, methodName[, implementation][, options])</code></a></li>
<li><span class="stability_1"><a href="#mockmodulespecifier-options"><code>mock.module(specifier[, options])</code></a></span></li>
<li><a href="#mockreset"><code>mock.reset()</code></a></li>
<li><a href="#mockrestoreall"><code>mock.restoreAll()</code></a></li>
<li><a href="#mocksetterobject-methodname-implementation-options"><code>mock.setter(object, methodName[, implementation][, options])</code></a></li>
</ul>
</li>
<li><span class="stability_1"><a href="#class-mocktimers">Class: <code>MockTimers</code></a></span>
<ul>
<li><a href="#timersenableenableoptions"><code>timers.enable([enableOptions])</code></a></li>
<li><a href="#timersreset"><code>timers.reset()</code></a></li>
<li><a href="#timerssymboldispose"><code>timers[Symbol.dispose]()</code></a></li>
<li><a href="#timerstickmilliseconds"><code>timers.tick([milliseconds])</code></a>
<ul>
<li><a href="#using-clear-functions">Using clear functions</a></li>
<li><a href="#working-with-nodejs-timers-modules">Working with Node.js timers modules</a></li>
</ul>
</li>
<li><a href="#timersrunall"><code>timers.runAll()</code></a></li>
<li><a href="#timerssettimemilliseconds"><code>timers.setTime(milliseconds)</code></a>
<ul>
<li><a href="#dates-and-timers-working-together">Dates and Timers working together</a></li>
</ul>
</li>
</ul>
</li>
<li><a href="#class-testsstream">Class: <code>TestsStream</code></a>
<ul>
<li><a href="#event-testcoverage">Event: <code>'test:coverage'</code></a></li>
<li><a href="#event-testcomplete">Event: <code>'test:complete'</code></a></li>
<li><a href="#event-testdequeue">Event: <code>'test:dequeue'</code></a></li>
<li><a href="#event-testdiagnostic">Event: <code>'test:diagnostic'</code></a></li>
<li><a href="#event-testenqueue">Event: <code>'test:enqueue'</code></a></li>
<li><a href="#event-testfail">Event: <code>'test:fail'</code></a></li>
<li><a href="#event-testpass">Event: <code>'test:pass'</code></a></li>
<li><a href="#event-testplan">Event: <code>'test:plan'</code></a></li>
<li><a href="#event-teststart">Event: <code>'test:start'</code></a></li>
<li><a href="#event-teststderr">Event: <code>'test:stderr'</code></a></li>
<li><a href="#event-teststdout">Event: <code>'test:stdout'</code></a></li>
<li><a href="#event-testsummary">Event: <code>'test:summary'</code></a></li>
<li><a href="#event-testwatchdrained">Event: <code>'test:watch:drained'</code></a></li>
</ul>
</li>
<li><a href="#class-testcontext">Class: <code>TestContext</code></a>
<ul>
<li><a href="#contextbeforefn-options"><code>context.before([fn][, options])</code></a></li>
<li><a href="#contextbeforeeachfn-options"><code>context.beforeEach([fn][, options])</code></a></li>
<li><a href="#contextafterfn-options"><code>context.after([fn][, options])</code></a></li>
<li><a href="#contextaftereachfn-options"><code>context.afterEach([fn][, options])</code></a></li>
<li><a href="#contextassert"><code>context.assert</code></a>
<ul>
<li><a href="#contextassertfilesnapshotvalue-path-options"><code>context.assert.fileSnapshot(value, path[, options])</code></a></li>
<li><a href="#contextassertsnapshotvalue-options"><code>context.assert.snapshot(value[, options])</code></a></li>
</ul>
</li>
<li><a href="#contextdiagnosticmessage"><code>context.diagnostic(message)</code></a></li>
<li><a href="#contextfilepath"><code>context.filePath</code></a></li>
<li><a href="#contextfullname"><code>context.fullName</code></a></li>
<li><a href="#contextname"><code>context.name</code></a></li>
<li><a href="#contextplancount"><code>context.plan(count)</code></a></li>
<li><a href="#contextrunonlyshouldrunonlytests"><code>context.runOnly(shouldRunOnlyTests)</code></a></li>
<li><a href="#contextsignal"><code>context.signal</code></a></li>
<li><a href="#contextskipmessage"><code>context.skip([message])</code></a></li>
<li><a href="#contexttodomessage"><code>context.todo([message])</code></a></li>
<li><a href="#contexttestname-options-fn"><code>context.test([name][, options][, fn])</code></a></li>
<li><a href="#contextwaitforcondition-options"><code>context.waitFor(condition[, options])</code></a></li>
</ul>
</li>
<li><a href="#class-suitecontext">Class: <code>SuiteContext</code></a>
<ul>
<li><a href="#contextfilepath_1"><code>context.filePath</code></a></li>
<li><a href="#contextname_1"><code>context.name</code></a></li>
<li><a href="#contextsignal_1"><code>context.signal</code></a></li>
</ul>
</li>
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      <details role="navigation" id="toc" open><summary>Table of contents</summary><ul>
<li><span class="stability_2"><a href="#test-runner">Test runner</a></span>
<ul>
<li><a href="#subtests">Subtests</a></li>
<li><a href="#skipping-tests">Skipping tests</a></li>
<li><a href="#todo-tests">TODO tests</a></li>
<li><a href="#describe-and-it-aliases"><code>describe()</code> and <code>it()</code> aliases</a></li>
<li><a href="#only-tests"><code>only</code> tests</a></li>
<li><a href="#filtering-tests-by-name">Filtering tests by name</a></li>
<li><a href="#extraneous-asynchronous-activity">Extraneous asynchronous activity</a></li>
<li><span class="stability_1"><a href="#watch-mode">Watch mode</a></span></li>
<li><a href="#running-tests-from-the-command-line">Running tests from the command line</a>
<ul>
<li><a href="#test-runner-execution-model">Test runner execution model</a></li>
</ul>
</li>
<li><span class="stability_1"><a href="#collecting-code-coverage">Collecting code coverage</a></span>
<ul>
<li><a href="#coverage-reporters">Coverage reporters</a></li>
</ul>
</li>
<li><a href="#mocking">Mocking</a>
<ul>
<li><a href="#timers">Timers</a></li>
<li><a href="#dates">Dates</a></li>
</ul>
</li>
<li><a href="#snapshot-testing">Snapshot testing</a></li>
<li><a href="#test-reporters">Test reporters</a>
<ul>
<li><a href="#custom-reporters">Custom reporters</a></li>
<li><a href="#multiple-reporters">Multiple reporters</a></li>
</ul>
</li>
<li><a href="#runoptions"><code>run([options])</code></a></li>
<li><a href="#suitename-options-fn"><code>suite([name][, options][, fn])</code></a></li>
<li><a href="#suiteskipname-options-fn"><code>suite.skip([name][, options][, fn])</code></a></li>
<li><a href="#suitetodoname-options-fn"><code>suite.todo([name][, options][, fn])</code></a></li>
<li><a href="#suiteonlyname-options-fn"><code>suite.only([name][, options][, fn])</code></a></li>
<li><a href="#testname-options-fn"><code>test([name][, options][, fn])</code></a></li>
<li><a href="#testskipname-options-fn"><code>test.skip([name][, options][, fn])</code></a></li>
<li><a href="#testtodoname-options-fn"><code>test.todo([name][, options][, fn])</code></a></li>
<li><a href="#testonlyname-options-fn"><code>test.only([name][, options][, fn])</code></a></li>
<li><a href="#describename-options-fn"><code>describe([name][, options][, fn])</code></a></li>
<li><a href="#describeskipname-options-fn"><code>describe.skip([name][, options][, fn])</code></a></li>
<li><a href="#describetodoname-options-fn"><code>describe.todo([name][, options][, fn])</code></a></li>
<li><a href="#describeonlyname-options-fn"><code>describe.only([name][, options][, fn])</code></a></li>
<li><a href="#itname-options-fn"><code>it([name][, options][, fn])</code></a></li>
<li><a href="#itskipname-options-fn"><code>it.skip([name][, options][, fn])</code></a></li>
<li><a href="#ittodoname-options-fn"><code>it.todo([name][, options][, fn])</code></a></li>
<li><a href="#itonlyname-options-fn"><code>it.only([name][, options][, fn])</code></a></li>
<li><a href="#beforefn-options"><code>before([fn][, options])</code></a></li>
<li><a href="#afterfn-options"><code>after([fn][, options])</code></a></li>
<li><a href="#beforeeachfn-options"><code>beforeEach([fn][, options])</code></a></li>
<li><a href="#aftereachfn-options"><code>afterEach([fn][, options])</code></a></li>
<li><a href="#assert"><code>assert</code></a>
<ul>
<li><a href="#assertregistername-fn"><code>assert.register(name, fn)</code></a></li>
</ul>
</li>
<li><a href="#snapshot"><code>snapshot</code></a>
<ul>
<li><a href="#snapshotsetdefaultsnapshotserializersserializers"><code>snapshot.setDefaultSnapshotSerializers(serializers)</code></a></li>
<li><a href="#snapshotsetresolvesnapshotpathfn"><code>snapshot.setResolveSnapshotPath(fn)</code></a></li>
</ul>
</li>
<li><a href="#class-mockfunctioncontext">Class: <code>MockFunctionContext</code></a>
<ul>
<li><a href="#ctxcalls"><code>ctx.calls</code></a></li>
<li><a href="#ctxcallcount"><code>ctx.callCount()</code></a></li>
<li><a href="#ctxmockimplementationimplementation"><code>ctx.mockImplementation(implementation)</code></a></li>
<li><a href="#ctxmockimplementationonceimplementation-oncall"><code>ctx.mockImplementationOnce(implementation[, onCall])</code></a></li>
<li><a href="#ctxresetcalls"><code>ctx.resetCalls()</code></a></li>
<li><a href="#ctxrestore"><code>ctx.restore()</code></a></li>
</ul>
</li>
<li><span class="stability_1"><a href="#class-mockmodulecontext">Class: <code>MockModuleContext</code></a></span>
<ul>
<li><a href="#ctxrestore_1"><code>ctx.restore()</code></a></li>
</ul>
</li>
<li><a href="#class-mocktracker">Class: <code>MockTracker</code></a>
<ul>
<li><a href="#mockfnoriginal-implementation-options"><code>mock.fn([original[, implementation]][, options])</code></a></li>
<li><a href="#mockgetterobject-methodname-implementation-options"><code>mock.getter(object, methodName[, implementation][, options])</code></a></li>
<li><a href="#mockmethodobject-methodname-implementation-options"><code>mock.method(object, methodName[, implementation][, options])</code></a></li>
<li><span class="stability_1"><a href="#mockmodulespecifier-options"><code>mock.module(specifier[, options])</code></a></span></li>
<li><a href="#mockreset"><code>mock.reset()</code></a></li>
<li><a href="#mockrestoreall"><code>mock.restoreAll()</code></a></li>
<li><a href="#mocksetterobject-methodname-implementation-options"><code>mock.setter(object, methodName[, implementation][, options])</code></a></li>
</ul>
</li>
<li><span class="stability_1"><a href="#class-mocktimers">Class: <code>MockTimers</code></a></span>
<ul>
<li><a href="#timersenableenableoptions"><code>timers.enable([enableOptions])</code></a></li>
<li><a href="#timersreset"><code>timers.reset()</code></a></li>
<li><a href="#timerssymboldispose"><code>timers[Symbol.dispose]()</code></a></li>
<li><a href="#timerstickmilliseconds"><code>timers.tick([milliseconds])</code></a>
<ul>
<li><a href="#using-clear-functions">Using clear functions</a></li>
<li><a href="#working-with-nodejs-timers-modules">Working with Node.js timers modules</a></li>
</ul>
</li>
<li><a href="#timersrunall"><code>timers.runAll()</code></a></li>
<li><a href="#timerssettimemilliseconds"><code>timers.setTime(milliseconds)</code></a>
<ul>
<li><a href="#dates-and-timers-working-together">Dates and Timers working together</a></li>
</ul>
</li>
</ul>
</li>
<li><a href="#class-testsstream">Class: <code>TestsStream</code></a>
<ul>
<li><a href="#event-testcoverage">Event: <code>'test:coverage'</code></a></li>
<li><a href="#event-testcomplete">Event: <code>'test:complete'</code></a></li>
<li><a href="#event-testdequeue">Event: <code>'test:dequeue'</code></a></li>
<li><a href="#event-testdiagnostic">Event: <code>'test:diagnostic'</code></a></li>
<li><a href="#event-testenqueue">Event: <code>'test:enqueue'</code></a></li>
<li><a href="#event-testfail">Event: <code>'test:fail'</code></a></li>
<li><a href="#event-testpass">Event: <code>'test:pass'</code></a></li>
<li><a href="#event-testplan">Event: <code>'test:plan'</code></a></li>
<li><a href="#event-teststart">Event: <code>'test:start'</code></a></li>
<li><a href="#event-teststderr">Event: <code>'test:stderr'</code></a></li>
<li><a href="#event-teststdout">Event: <code>'test:stdout'</code></a></li>
<li><a href="#event-testsummary">Event: <code>'test:summary'</code></a></li>
<li><a href="#event-testwatchdrained">Event: <code>'test:watch:drained'</code></a></li>
</ul>
</li>
<li><a href="#class-testcontext">Class: <code>TestContext</code></a>
<ul>
<li><a href="#contextbeforefn-options"><code>context.before([fn][, options])</code></a></li>
<li><a href="#contextbeforeeachfn-options"><code>context.beforeEach([fn][, options])</code></a></li>
<li><a href="#contextafterfn-options"><code>context.after([fn][, options])</code></a></li>
<li><a href="#contextaftereachfn-options"><code>context.afterEach([fn][, options])</code></a></li>
<li><a href="#contextassert"><code>context.assert</code></a>
<ul>
<li><a href="#contextassertfilesnapshotvalue-path-options"><code>context.assert.fileSnapshot(value, path[, options])</code></a></li>
<li><a href="#contextassertsnapshotvalue-options"><code>context.assert.snapshot(value[, options])</code></a></li>
</ul>
</li>
<li><a href="#contextdiagnosticmessage"><code>context.diagnostic(message)</code></a></li>
<li><a href="#contextfilepath"><code>context.filePath</code></a></li>
<li><a href="#contextfullname"><code>context.fullName</code></a></li>
<li><a href="#contextname"><code>context.name</code></a></li>
<li><a href="#contextplancount"><code>context.plan(count)</code></a></li>
<li><a href="#contextrunonlyshouldrunonlytests"><code>context.runOnly(shouldRunOnlyTests)</code></a></li>
<li><a href="#contextsignal"><code>context.signal</code></a></li>
<li><a href="#contextskipmessage"><code>context.skip([message])</code></a></li>
<li><a href="#contexttodomessage"><code>context.todo([message])</code></a></li>
<li><a href="#contexttestname-options-fn"><code>context.test([name][, options][, fn])</code></a></li>
<li><a href="#contextwaitforcondition-options"><code>context.waitFor(condition[, options])</code></a></li>
</ul>
</li>
<li><a href="#class-suitecontext">Class: <code>SuiteContext</code></a>
<ul>
<li><a href="#contextfilepath_1"><code>context.filePath</code></a></li>
<li><a href="#contextname_1"><code>context.name</code></a></li>
<li><a href="#contextsignal_1"><code>context.signal</code></a></li>
</ul>
</li>
</ul>
</li>
</ul></details>

      <div role="main" id="apicontent">
        <h2>Test runner<span><a class="mark" href="#test-runner" id="test-runner">#</a></span><a aria-hidden="true" class="legacy" id="test_test_runner"></a></h2>

<div class="api_metadata">
<details class="changelog"><summary>History</summary>
<table>
<tbody><tr><th>Version</th><th>Changes</th></tr>
<tr><td>v20.0.0</td>
<td><p>The test runner is now stable.</p></td></tr>
<tr><td>v18.0.0, v16.17.0</td>
<td><p><span>Added in: v18.0.0, v16.17.0</span></p></td></tr>
</tbody></table>
</details>
</div>
<p></p><div class="api_stability api_stability_2"><a href="documentation.html#stability-index">Stability: 2</a> - Stable</div><p></p>
<p><strong>Source Code:</strong> <a href="https://github.com/nodejs/node/blob/v22.14.0/lib/test.js">lib/test.js</a></p>
<p>The <code>node:test</code> module facilitates the creation of JavaScript tests.
To access it:</p>

<pre class="with-34-chars"><input class="js-flavor-toggle" type="checkbox" checked aria-label="Show modern ES modules syntax"><code class="language-js mjs"><span class="hljs-keyword">import</span> test <span class="hljs-keyword">from</span> <span class="hljs-string">'node:test'</span>;</code><code class="language-js cjs"><span class="hljs-keyword">const</span> test = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:test'</span>);</code><button class="copy-button">copy</button></pre>
<p>This module is only available under the <code>node:</code> scheme.</p>
<p>Tests created via the <code>test</code> module consist of a single function that is
processed in one of three ways:</p>
<ol>
<li>A synchronous function that is considered failing if it throws an exception,
and is considered passing otherwise.</li>
<li>A function that returns a <code>Promise</code> that is considered failing if the
<code>Promise</code> rejects, and is considered passing if the <code>Promise</code> fulfills.</li>
<li>A function that receives a callback function. If the callback receives any
truthy value as its first argument, the test is considered failing. If a
falsy value is passed as the first argument to the callback, the test is
considered passing. If the test function receives a callback function and
also returns a <code>Promise</code>, the test will fail.</li>
</ol>
<p>The following example illustrates how tests are written using the
<code>test</code> module.</p>
<pre><code class="language-js"><span class="hljs-title function_">test</span>(<span class="hljs-string">'synchronous passing test'</span>, <span class="hljs-function">(<span class="hljs-params">t</span>) =></span> {
  <span class="hljs-comment">// This test passes because it does not throw an exception.</span>
  assert.<span class="hljs-title function_">strictEqual</span>(<span class="hljs-number">1</span>, <span class="hljs-number">1</span>);
});

<span class="hljs-title function_">test</span>(<span class="hljs-string">'synchronous failing test'</span>, <span class="hljs-function">(<span class="hljs-params">t</span>) =></span> {
  <span class="hljs-comment">// This test fails because it throws an exception.</span>
  assert.<span class="hljs-title function_">strictEqual</span>(<span class="hljs-number">1</span>, <span class="hljs-number">2</span>);
});

<span class="hljs-title function_">test</span>(<span class="hljs-string">'asynchronous passing test'</span>, <span class="hljs-title function_">async</span> (t) => {
  <span class="hljs-comment">// This test passes because the Promise returned by the async</span>
  <span class="hljs-comment">// function is settled and not rejected.</span>
  assert.<span class="hljs-title function_">strictEqual</span>(<span class="hljs-number">1</span>, <span class="hljs-number">1</span>);
});

<span class="hljs-title function_">test</span>(<span class="hljs-string">'asynchronous failing test'</span>, <span class="hljs-title function_">async</span> (t) => {
  <span class="hljs-comment">// This test fails because the Promise returned by the async</span>
  <span class="hljs-comment">// function is rejected.</span>
  assert.<span class="hljs-title function_">strictEqual</span>(<span class="hljs-number">1</span>, <span class="hljs-number">2</span>);
});

<span class="hljs-title function_">test</span>(<span class="hljs-string">'failing test using Promises'</span>, <span class="hljs-function">(<span class="hljs-params">t</span>) =></span> {
  <span class="hljs-comment">// Promises can be used directly as well.</span>
  <span class="hljs-keyword">return</span> <span class="hljs-keyword">new</span> <span class="hljs-title class_">Promise</span>(<span class="hljs-function">(<span class="hljs-params">resolve, reject</span>) =></span> {
    <span class="hljs-title function_">setImmediate</span>(<span class="hljs-function">() =></span> {
      <span class="hljs-title function_">reject</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">Error</span>(<span class="hljs-string">'this will cause the test to fail'</span>));
    });
  });
});

<span class="hljs-title function_">test</span>(<span class="hljs-string">'callback passing test'</span>, <span class="hljs-function">(<span class="hljs-params">t, done</span>) =></span> {
  <span class="hljs-comment">// done() is the callback function. When the setImmediate() runs, it invokes</span>
  <span class="hljs-comment">// done() with no arguments.</span>
  <span class="hljs-title function_">setImmediate</span>(done);
});

<span class="hljs-title function_">test</span>(<span class="hljs-string">'callback failing test'</span>, <span class="hljs-function">(<span class="hljs-params">t, done</span>) =></span> {
  <span class="hljs-comment">// When the setImmediate() runs, done() is invoked with an Error object and</span>
  <span class="hljs-comment">// the test fails.</span>
  <span class="hljs-title function_">setImmediate</span>(<span class="hljs-function">() =></span> {
    <span class="hljs-title function_">done</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">Error</span>(<span class="hljs-string">'callback failure'</span>));
  });
});</code> <button class="copy-button">copy</button></pre>
<p>If any tests fail, the process exit code is set to <code>1</code>.</p>
<section><h3>Subtests<span><a class="mark" href="#subtests" id="subtests">#</a></span><a aria-hidden="true" class="legacy" id="test_subtests"></a></h3>
<p>The test context's <code>test()</code> method allows subtests to be created.
It allows you to structure your tests in a hierarchical manner,
where you can create nested tests within a larger test.
This method behaves identically to the top level <code>test()</code> function.
The following example demonstrates the creation of a
top level test with two subtests.</p>
<pre><code class="language-js"><span class="hljs-title function_">test</span>(<span class="hljs-string">'top level test'</span>, <span class="hljs-title function_">async</span> (t) => {
  <span class="hljs-keyword">await</span> t.<span class="hljs-title function_">test</span>(<span class="hljs-string">'subtest 1'</span>, <span class="hljs-function">(<span class="hljs-params">t</span>) =></span> {
    assert.<span class="hljs-title function_">strictEqual</span>(<span class="hljs-number">1</span>, <span class="hljs-number">1</span>);
  });

  <span class="hljs-keyword">await</span> t.<span class="hljs-title function_">test</span>(<span class="hljs-string">'subtest 2'</span>, <span class="hljs-function">(<span class="hljs-params">t</span>) =></span> {
    assert.<span class="hljs-title function_">strictEqual</span>(<span class="hljs-number">2</span>, <span class="hljs-number">2</span>);
  });
});</code> <button class="copy-button">copy</button></pre>
<blockquote>
<p><strong>Note:</strong> <code>beforeEach</code> and <code>afterEach</code> hooks are triggered
between each subtest execution.</p>
</blockquote>
<p>In this example, <code>await</code> is used to ensure that both subtests have completed.
This is necessary because tests do not wait for their subtests to
complete, unlike tests created within suites.
Any subtests that are still outstanding when their parent finishes
are cancelled and treated as failures. Any subtest failures cause the parent
test to fail.</p>
</section><section><h3>Skipping tests<span><a class="mark" href="#skipping-tests" id="skipping-tests">#</a></span><a aria-hidden="true" class="legacy" id="test_skipping_tests"></a></h3>
<p>Individual tests can be skipped by passing the <code>skip</code> option to the test, or by
calling the test context's <code>skip()</code> method as shown in the
following example.</p>
<pre><code class="language-js"><span class="hljs-comment">// The skip option is used, but no message is provided.</span>
<span class="hljs-title function_">test</span>(<span class="hljs-string">'skip option'</span>, { <span class="hljs-attr">skip</span>: <span class="hljs-literal">true</span> }, <span class="hljs-function">(<span class="hljs-params">t</span>) =></span> {
  <span class="hljs-comment">// This code is never executed.</span>
});

<span class="hljs-comment">// The skip option is used, and a message is provided.</span>
<span class="hljs-title function_">test</span>(<span class="hljs-string">'skip option with message'</span>, { <span class="hljs-attr">skip</span>: <span class="hljs-string">'this is skipped'</span> }, <span class="hljs-function">(<span class="hljs-params">t</span>) =></span> {
  <span class="hljs-comment">// This code is never executed.</span>
});

<span class="hljs-title function_">test</span>(<span class="hljs-string">'skip() method'</span>, <span class="hljs-function">(<span class="hljs-params">t</span>) =></span> {
  <span class="hljs-comment">// Make sure to return here as well if the test contains additional logic.</span>
  t.<span class="hljs-title function_">skip</span>();
});

<span class="hljs-title function_">test</span>(<span class="hljs-string">'skip() method with message'</span>, <span class="hljs-function">(<span class="hljs-params">t</span>) =></span> {
  <span class="hljs-comment">// Make sure to return here as well if the test contains additional logic.</span>
  t.<span class="hljs-title function_">skip</span>(<span class="hljs-string">'this is skipped'</span>);
});</code> <button class="copy-button">copy</button></pre>
</section><section><h3>TODO tests<span><a class="mark" href="#todo-tests" id="todo-tests">#</a></span><a aria-hidden="true" class="legacy" id="test_todo_tests"></a></h3>
<p>Individual tests can be marked as flaky or incomplete by passing the <code>todo</code>
option to the test, or by calling the test context's <code>todo()</code> method, as shown
in the following example. These tests represent a pending implementation or bug
that needs to be fixed. TODO tests are executed, but are not treated as test
failures, and therefore do not affect the process exit code. If a test is marked
as both TODO and skipped, the TODO option is ignored.</p>
<pre><code class="language-js"><span class="hljs-comment">// The todo option is used, but no message is provided.</span>
<span class="hljs-title function_">test</span>(<span class="hljs-string">'todo option'</span>, { <span class="hljs-attr">todo</span>: <span class="hljs-literal">true</span> }, <span class="hljs-function">(<span class="hljs-params">t</span>) =></span> {
  <span class="hljs-comment">// This code is executed, but not treated as a failure.</span>
  <span class="hljs-keyword">throw</span> <span class="hljs-keyword">new</span> <span class="hljs-title class_">Error</span>(<span class="hljs-string">'this does not fail the test'</span>);
});

<span class="hljs-comment">// The todo option is used, and a message is provided.</span>
<span class="hljs-title function_">test</span>(<span class="hljs-string">'todo option with message'</span>, { <span class="hljs-attr">todo</span>: <span class="hljs-string">'this is a todo test'</span> }, <span class="hljs-function">(<span class="hljs-params">t</span>) =></span> {
  <span class="hljs-comment">// This code is executed.</span>
});

<span class="hljs-title function_">test</span>(<span class="hljs-string">'todo() method'</span>, <span class="hljs-function">(<span class="hljs-params">t</span>) =></span> {
  t.<span class="hljs-title function_">todo</span>();
});

<span class="hljs-title function_">test</span>(<span class="hljs-string">'todo() method with message'</span>, <span class="hljs-function">(<span class="hljs-params">t</span>) =></span> {
  t.<span class="hljs-title function_">todo</span>(<span class="hljs-string">'this is a todo test and is not treated as a failure'</span>);
  <span class="hljs-keyword">throw</span> <span class="hljs-keyword">new</span> <span class="hljs-title class_">Error</span>(<span class="hljs-string">'this does not fail the test'</span>);
});</code> <button class="copy-button">copy</button></pre>
</section><section><h3><code>describe()</code> and <code>it()</code> aliases<span><a class="mark" href="#describe-and-it-aliases" id="describe-and-it-aliases">#</a></span><a aria-hidden="true" class="legacy" id="test_describe_and_it_aliases"></a></h3>
<p>Suites and tests can also be written using the <code>describe()</code> and <code>it()</code>
functions. <a href="#describename-options-fn"><code>describe()</code></a> is an alias for <a href="#suitename-options-fn"><code>suite()</code></a>, and <a href="#itname-options-fn"><code>it()</code></a> is an
alias for <a href="#testname-options-fn"><code>test()</code></a>.</p>
<pre><code class="language-js"><span class="hljs-title function_">describe</span>(<span class="hljs-string">'A thing'</span>, <span class="hljs-function">() =></span> {
  <span class="hljs-title function_">it</span>(<span class="hljs-string">'should work'</span>, <span class="hljs-function">() =></span> {
    assert.<span class="hljs-title function_">strictEqual</span>(<span class="hljs-number">1</span>, <span class="hljs-number">1</span>);
  });

  <span class="hljs-title function_">it</span>(<span class="hljs-string">'should be ok'</span>, <span class="hljs-function">() =></span> {
    assert.<span class="hljs-title function_">strictEqual</span>(<span class="hljs-number">2</span>, <span class="hljs-number">2</span>);
  });

  <span class="hljs-title function_">describe</span>(<span class="hljs-string">'a nested thing'</span>, <span class="hljs-function">() =></span> {
    <span class="hljs-title function_">it</span>(<span class="hljs-string">'should work'</span>, <span class="hljs-function">() =></span> {
      assert.<span class="hljs-title function_">strictEqual</span>(<span class="hljs-number">3</span>, <span class="hljs-number">3</span>);
    });
  });
});</code> <button class="copy-button">copy</button></pre>
<p><code>describe()</code> and <code>it()</code> are imported from the <code>node:test</code> module.</p>

<pre class="with-46-chars"><input class="js-flavor-toggle" type="checkbox" checked aria-label="Show modern ES modules syntax"><code class="language-js mjs"><span class="hljs-keyword">import</span> { describe, it } <span class="hljs-keyword">from</span> <span class="hljs-string">'node:test'</span>;</code><code class="language-js cjs"><span class="hljs-keyword">const</span> { describe, it } = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:test'</span>);</code><button class="copy-button">copy</button></pre>
</section><section><h3><code>only</code> tests<span><a class="mark" href="#only-tests" id="only-tests">#</a></span><a aria-hidden="true" class="legacy" id="test_only_tests"></a></h3>
<p>If Node.js is started with the <a href="cli.html#--test-only"><code>--test-only</code></a> command-line option, or test
isolation is disabled, it is possible to skip all tests except for a selected
subset by passing the <code>only</code> option to the tests that should run. When a test
with the <code>only</code> option is set, all subtests are also run.
If a suite has the <code>only</code> option set, all tests within the suite are run,
unless it has descendants with the <code>only</code> option set, in which case only those
tests are run.</p>
<p>When using <a href="#subtests">subtests</a> within a <code>test()</code>/<code>it()</code>, it is required to mark
all ancestor tests with the <code>only</code> option to run only a
selected subset of tests.</p>
<p>The test context's <code>runOnly()</code>
method can be used to implement the same behavior at the subtest level. Tests
that are not executed are omitted from the test runner output.</p>
<pre><code class="language-js"><span class="hljs-comment">// Assume Node.js is run with the --test-only command-line option.</span>
<span class="hljs-comment">// The suite's 'only' option is set, so these tests are run.</span>
<span class="hljs-title function_">test</span>(<span class="hljs-string">'this test is run'</span>, { <span class="hljs-attr">only</span>: <span class="hljs-literal">true</span> }, <span class="hljs-title function_">async</span> (t) => {
  <span class="hljs-comment">// Within this test, all subtests are run by default.</span>
  <span class="hljs-keyword">await</span> t.<span class="hljs-title function_">test</span>(<span class="hljs-string">'running subtest'</span>);

  <span class="hljs-comment">// The test context can be updated to run subtests with the 'only' option.</span>
  t.<span class="hljs-title function_">runOnly</span>(<span class="hljs-literal">true</span>);
  <span class="hljs-keyword">await</span> t.<span class="hljs-title function_">test</span>(<span class="hljs-string">'this subtest is now skipped'</span>);
  <span class="hljs-keyword">await</span> t.<span class="hljs-title function_">test</span>(<span class="hljs-string">'this subtest is run'</span>, { <span class="hljs-attr">only</span>: <span class="hljs-literal">true</span> });

  <span class="hljs-comment">// Switch the context back to execute all tests.</span>
  t.<span class="hljs-title function_">runOnly</span>(<span class="hljs-literal">false</span>);
  <span class="hljs-keyword">await</span> t.<span class="hljs-title function_">test</span>(<span class="hljs-string">'this subtest is now run'</span>);

  <span class="hljs-comment">// Explicitly do not run these tests.</span>
  <span class="hljs-keyword">await</span> t.<span class="hljs-title function_">test</span>(<span class="hljs-string">'skipped subtest 3'</span>, { <span class="hljs-attr">only</span>: <span class="hljs-literal">false</span> });
  <span class="hljs-keyword">await</span> t.<span class="hljs-title function_">test</span>(<span class="hljs-string">'skipped subtest 4'</span>, { <span class="hljs-attr">skip</span>: <span class="hljs-literal">true</span> });
});

<span class="hljs-comment">// The 'only' option is not set, so this test is skipped.</span>
<span class="hljs-title function_">test</span>(<span class="hljs-string">'this test is not run'</span>, <span class="hljs-function">() =></span> {
  <span class="hljs-comment">// This code is not run.</span>
  <span class="hljs-keyword">throw</span> <span class="hljs-keyword">new</span> <span class="hljs-title class_">Error</span>(<span class="hljs-string">'fail'</span>);
});

<span class="hljs-title function_">describe</span>(<span class="hljs-string">'a suite'</span>, <span class="hljs-function">() =></span> {
  <span class="hljs-comment">// The 'only' option is set, so this test is run.</span>
  <span class="hljs-title function_">it</span>(<span class="hljs-string">'this test is run'</span>, { <span class="hljs-attr">only</span>: <span class="hljs-literal">true</span> }, <span class="hljs-function">() =></span> {
    <span class="hljs-comment">// This code is run.</span>
  });

  <span class="hljs-title function_">it</span>(<span class="hljs-string">'this test is not run'</span>, <span class="hljs-function">() =></span> {
    <span class="hljs-comment">// This code is not run.</span>
    <span class="hljs-keyword">throw</span> <span class="hljs-keyword">new</span> <span class="hljs-title class_">Error</span>(<span class="hljs-string">'fail'</span>);
  });
});

describe.<span class="hljs-title function_">only</span>(<span class="hljs-string">'a suite'</span>, <span class="hljs-function">() =></span> {
  <span class="hljs-comment">// The 'only' option is set, so this test is run.</span>
  <span class="hljs-title function_">it</span>(<span class="hljs-string">'this test is run'</span>, <span class="hljs-function">() =></span> {
    <span class="hljs-comment">// This code is run.</span>
  });

  <span class="hljs-title function_">it</span>(<span class="hljs-string">'this test is run'</span>, <span class="hljs-function">() =></span> {
    <span class="hljs-comment">// This code is run.</span>
  });
});</code> <button class="copy-button">copy</button></pre>
</section><section><h3>Filtering tests by name<span><a class="mark" href="#filtering-tests-by-name" id="filtering-tests-by-name">#</a></span><a aria-hidden="true" class="legacy" id="test_filtering_tests_by_name"></a></h3>
<p>The <a href="cli.html#--test-name-pattern"><code>--test-name-pattern</code></a> command-line option can be used to only run
tests whose name matches the provided pattern, and the
<a href="cli.html#--test-skip-pattern"><code>--test-skip-pattern</code></a> option can be used to skip tests whose name
matches the provided pattern. Test name patterns are interpreted as
JavaScript regular expressions. The <code>--test-name-pattern</code> and
<code>--test-skip-pattern</code> options can be specified multiple times in order to run
nested tests. For each test that is executed, any corresponding test hooks,
such as <code>beforeEach()</code>, are also run. Tests that are not executed are omitted
from the test runner output.</p>
<p>Given the following test file, starting Node.js with the
<code>--test-name-pattern="test [1-3]"</code> option would cause the test runner to execute
<code>test 1</code>, <code>test 2</code>, and <code>test 3</code>. If <code>test 1</code> did not match the test name
pattern, then its subtests would not execute, despite matching the pattern. The
same set of tests could also be executed by passing <code>--test-name-pattern</code>
multiple times (e.g. <code>--test-name-pattern="test 1"</code>,
<code>--test-name-pattern="test 2"</code>, etc.).</p>
<pre><code class="language-js"><span class="hljs-title function_">test</span>(<span class="hljs-string">'test 1'</span>, <span class="hljs-title function_">async</span> (t) => {
  <span class="hljs-keyword">await</span> t.<span class="hljs-title function_">test</span>(<span class="hljs-string">'test 2'</span>);
  <span class="hljs-keyword">await</span> t.<span class="hljs-title function_">test</span>(<span class="hljs-string">'test 3'</span>);
});

<span class="hljs-title function_">test</span>(<span class="hljs-string">'Test 4'</span>, <span class="hljs-title function_">async</span> (t) => {
  <span class="hljs-keyword">await</span> t.<span class="hljs-title function_">test</span>(<span class="hljs-string">'Test 5'</span>);
  <span class="hljs-keyword">await</span> t.<span class="hljs-title function_">test</span>(<span class="hljs-string">'test 6'</span>);
});</code> <button class="copy-button">copy</button></pre>
<p>Test name patterns can also be specified using regular expression literals. This
allows regular expression flags to be used. In the previous example, starting
Node.js with <code>--test-name-pattern="/test [4-5]/i"</code> (or <code>--test-skip-pattern="/test [4-5]/i"</code>)
would match <code>Test 4</code> and <code>Test 5</code> because the pattern is case-insensitive.</p>
<p>To match a single test with a pattern, you can prefix it with all its ancestor
test names separated by space, to ensure it is unique.
For example, given the following test file:</p>
<pre><code class="language-js"><span class="hljs-title function_">describe</span>(<span class="hljs-string">'test 1'</span>, <span class="hljs-function">(<span class="hljs-params">t</span>) =></span> {
  <span class="hljs-title function_">it</span>(<span class="hljs-string">'some test'</span>);
});

<span class="hljs-title function_">describe</span>(<span class="hljs-string">'test 2'</span>, <span class="hljs-function">(<span class="hljs-params">t</span>) =></span> {
  <span class="hljs-title function_">it</span>(<span class="hljs-string">'some test'</span>);
});</code> <button class="copy-button">copy</button></pre>
<p>Starting Node.js with <code>--test-name-pattern="test 1 some test"</code> would match
only <code>some test</code> in <code>test 1</code>.</p>
<p>Test name patterns do not change the set of files that the test runner executes.</p>
<p>If both <code>--test-name-pattern</code> and <code>--test-skip-pattern</code> are supplied,
tests must satisfy <strong>both</strong> requirements in order to be executed.</p>
</section><section><h3>Extraneous asynchronous activity<span><a class="mark" href="#extraneous-asynchronous-activity" id="extraneous-asynchronous-activity">#</a></span><a aria-hidden="true" class="legacy" id="test_extraneous_asynchronous_activity"></a></h3>
<p>Once a test function finishes executing, the results are reported as quickly
as possible while maintaining the order of the tests. However, it is possible
for the test function to generate asynchronous activity that outlives the test
itself. The test runner handles this type of activity, but does not delay the
reporting of test results in order to accommodate it.</p>
<p>In the following example, a test completes with two <code>setImmediate()</code>
operations still outstanding. The first <code>setImmediate()</code> attempts to create a
new subtest. Because the parent test has already finished and output its
results, the new subtest is immediately marked as failed, and reported later
to the <a href="test.html#class-testsstream" class="type">&#x3C;TestsStream></a>.</p>
<p>The second <code>setImmediate()</code> creates an <code>uncaughtException</code> event.
<code>uncaughtException</code> and <code>unhandledRejection</code> events originating from a completed
test are marked as failed by the <code>test</code> module and reported as diagnostic
warnings at the top level by the <a href="test.html#class-testsstream" class="type">&#x3C;TestsStream></a>.</p>
<pre><code class="language-js"><span class="hljs-title function_">test</span>(<span class="hljs-string">'a test that creates asynchronous activity'</span>, <span class="hljs-function">(<span class="hljs-params">t</span>) =></span> {
  <span class="hljs-title function_">setImmediate</span>(<span class="hljs-function">() =></span> {
    t.<span class="hljs-title function_">test</span>(<span class="hljs-string">'subtest that is created too late'</span>, <span class="hljs-function">(<span class="hljs-params">t</span>) =></span> {
      <span class="hljs-keyword">throw</span> <span class="hljs-keyword">new</span> <span class="hljs-title class_">Error</span>(<span class="hljs-string">'error1'</span>);
    });
  });

  <span class="hljs-title function_">setImmediate</span>(<span class="hljs-function">() =></span> {
    <span class="hljs-keyword">throw</span> <span class="hljs-keyword">new</span> <span class="hljs-title class_">Error</span>(<span class="hljs-string">'error2'</span>);
  });

  <span class="hljs-comment">// The test finishes after this line.</span>
});</code> <button class="copy-button">copy</button></pre>
</section><section><h3>Watch mode<span><a class="mark" href="#watch-mode" id="watch-mode">#</a></span><a aria-hidden="true" class="legacy" id="test_watch_mode"></a></h3>
<div class="api_metadata">
<span>Added in: v19.2.0, v18.13.0</span>
</div>
<p></p><div class="api_stability api_stability_1"><a href="documentation.html#stability-index">Stability: 1</a> - Experimental</div><p></p>
<p>The Node.js test runner supports running in watch mode by passing the <code>--watch</code> flag:</p>
<pre><code class="language-bash">node --<span class="hljs-built_in">test</span> --watch</code> <button class="copy-button">copy</button></pre>
<p>In watch mode, the test runner will watch for changes to test files and
their dependencies. When a change is detected, the test runner will
rerun the tests affected by the change.
The test runner will continue to run until the process is terminated.</p>
</section><section><h3>Running tests from the command line<span><a class="mark" href="#running-tests-from-the-command-line" id="running-tests-from-the-command-line">#</a></span><a aria-hidden="true" class="legacy" id="test_running_tests_from_the_command_line"></a></h3>
<p>The Node.js test runner can be invoked from the command line by passing the
<a href="cli.html#--test"><code>--test</code></a> flag:</p>
<pre><code class="language-bash">node --<span class="hljs-built_in">test</span></code> <button class="copy-button">copy</button></pre>
<p>By default, Node.js will run all files matching these patterns:</p>
<ul>
<li><code>**/*.test.{cjs,mjs,js}</code></li>
<li><code>**/*-test.{cjs,mjs,js}</code></li>
<li><code>**/*_test.{cjs,mjs,js}</code></li>
<li><code>**/test-*.{cjs,mjs,js}</code></li>
<li><code>**/test.{cjs,mjs,js}</code></li>
<li><code>**/test/**/*.{cjs,mjs,js}</code></li>
</ul>
<p>When <a href="cli.html#--experimental-strip-types"><code>--experimental-strip-types</code></a> is supplied, the following
additional patterns are matched:</p>
<ul>
<li><code>**/*.test.{cts,mts,ts}</code></li>
<li><code>**/*-test.{cts,mts,ts}</code></li>
<li><code>**/*_test.{cts,mts,ts}</code></li>
<li><code>**/test-*.{cts,mts,ts}</code></li>
<li><code>**/test.{cts,mts,ts}</code></li>
<li><code>**/test/**/*.{cts,mts,ts}</code></li>
</ul>
<p>Alternatively, one or more glob patterns can be provided as the
final argument(s) to the Node.js command, as shown below.
Glob patterns follow the behavior of <a href="https://man7.org/linux/man-pages/man7/glob.7.html"><code>glob(7)</code></a>.
The glob patterns should be enclosed in double quotes on the command line to
prevent shell expansion, which can reduce portability across systems.</p>
<pre><code class="language-bash">node --<span class="hljs-built_in">test</span> <span class="hljs-string">"**/*.test.js"</span> <span class="hljs-string">"**/*.spec.js"</span></code> <button class="copy-button">copy</button></pre>
<p>Matching files are executed as test files.
More information on the test file execution can be found
in the <a href="#test-runner-execution-model">test runner execution model</a> section.</p>
<h4>Test runner execution model<span><a class="mark" href="#test-runner-execution-model" id="test-runner-execution-model">#</a></span><a aria-hidden="true" class="legacy" id="test_test_runner_execution_model"></a></h4>
<p>When process-level test isolation is enabled, each matching test file is
executed in a separate child process. The maximum number of child processes
running at any time is controlled by the <a href="cli.html#--test-concurrency"><code>--test-concurrency</code></a> flag. If the
child process finishes with an exit code of 0, the test is considered passing.
Otherwise, the test is considered to be a failure. Test files must be executable
by Node.js, but are not required to use the <code>node:test</code> module internally.</p>
<p>Each test file is executed as if it was a regular script. That is, if the test
file itself uses <code>node:test</code> to define tests, all of those tests will be
executed within a single application thread, regardless of the value of the
<code>concurrency</code> option of <a href="#testname-options-fn"><code>test()</code></a>.</p>
<p>When process-level test isolation is disabled, each matching test file is
imported into the test runner process. Once all test files have been loaded, the
top level tests are executed with a concurrency of one. Because the test files
are all run within the same context, it is possible for tests to interact with
each other in ways that are not possible when isolation is enabled. For example,
if a test relies on global state, it is possible for that state to be modified
by a test originating from another file.</p>
</section><section><h3>Collecting code coverage<span><a class="mark" href="#collecting-code-coverage" id="collecting-code-coverage">#</a></span><a aria-hidden="true" class="legacy" id="test_collecting_code_coverage"></a></h3>
<p></p><div class="api_stability api_stability_1"><a href="documentation.html#stability-index">Stability: 1</a> - Experimental</div><p></p>
<p>When Node.js is started with the <a href="cli.html#--experimental-test-coverage"><code>--experimental-test-coverage</code></a>
command-line flag, code coverage is collected and statistics are reported once
all tests have completed. If the <a href="cli.html#node_v8_coveragedir"><code>NODE_V8_COVERAGE</code></a> environment variable is
used to specify a code coverage directory, the generated V8 coverage files are
written to that directory. Node.js core modules and files within
<code>node_modules/</code> directories are, by default, not included in the coverage report.
However, they can be explicitly included via the <a href="cli.html#--test-coverage-include"><code>--test-coverage-include</code></a> flag. If
coverage is enabled, the coverage report is sent to any <a href="#test-reporters">test reporters</a> via
the <code>'test:coverage'</code> event.</p>
<p>Coverage can be disabled on a series of lines using the following
comment syntax:</p>
<pre><code class="language-js"><span class="hljs-comment">/* node:coverage disable */</span>
<span class="hljs-keyword">if</span> (anAlwaysFalseCondition) {
  <span class="hljs-comment">// Code in this branch will never be executed, but the lines are ignored for</span>
  <span class="hljs-comment">// coverage purposes. All lines following the 'disable' comment are ignored</span>
  <span class="hljs-comment">// until a corresponding 'enable' comment is encountered.</span>
  <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(<span class="hljs-string">'this is never executed'</span>);
}
<span class="hljs-comment">/* node:coverage enable */</span></code> <button class="copy-button">copy</button></pre>
<p>Coverage can also be disabled for a specified number of lines. After the
specified number of lines, coverage will be automatically reenabled. If the
number of lines is not explicitly provided, a single line is ignored.</p>
<pre><code class="language-js"><span class="hljs-comment">/* node:coverage ignore next */</span>
<span class="hljs-keyword">if</span> (anAlwaysFalseCondition) { <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(<span class="hljs-string">'this is never executed'</span>); }

<span class="hljs-comment">/* node:coverage ignore next 3 */</span>
<span class="hljs-keyword">if</span> (anAlwaysFalseCondition) {
  <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(<span class="hljs-string">'this is never executed'</span>);
}</code> <button class="copy-button">copy</button></pre>
<h4>Coverage reporters<span><a class="mark" href="#coverage-reporters" id="coverage-reporters">#</a></span><a aria-hidden="true" class="legacy" id="test_coverage_reporters"></a></h4>
<p>The tap and spec reporters will print a summary of the coverage statistics.
There is also an lcov reporter that will generate an lcov file which can be
used as an in depth coverage report.</p>
<pre><code class="language-bash">node --<span class="hljs-built_in">test</span> --experimental-test-coverage --test-reporter=lcov --test-reporter-destination=lcov.info</code> <button class="copy-button">copy</button></pre>
<ul>
<li>No test results are reported by this reporter.</li>
<li>This reporter should ideally be used alongside another reporter.</li>
</ul>
</section><section><h3>Mocking<span><a class="mark" href="#mocking" id="mocking">#</a></span><a aria-hidden="true" class="legacy" id="test_mocking"></a></h3>
<p>The <code>node:test</code> module supports mocking during testing via a top-level <code>mock</code>
object. The following example creates a spy on a function that adds two numbers
together. The spy is then used to assert that the function was called as
expected.</p>

<pre class="with-39-chars"><input class="js-flavor-toggle" type="checkbox" checked aria-label="Show modern ES modules syntax"><code class="language-js mjs"><span class="hljs-keyword">import</span> assert <span class="hljs-keyword">from</span> <span class="hljs-string">'node:assert'</span>;
<span class="hljs-keyword">import</span> { mock, test } <span class="hljs-keyword">from</span> <span class="hljs-string">'node:test'</span>;

<span class="hljs-title function_">test</span>(<span class="hljs-string">'spies on a function'</span>, <span class="hljs-function">() =></span> {
  <span class="hljs-keyword">const</span> sum = mock.<span class="hljs-title function_">fn</span>(<span class="hljs-function">(<span class="hljs-params">a, b</span>) =></span> {
    <span class="hljs-keyword">return</span> a + b;
  });

  assert.<span class="hljs-title function_">strictEqual</span>(sum.<span class="hljs-property">mock</span>.<span class="hljs-title function_">callCount</span>(), <span class="hljs-number">0</span>);
  assert.<span class="hljs-title function_">strictEqual</span>(<span class="hljs-title function_">sum</span>(<span class="hljs-number">3</span>, <span class="hljs-number">4</span>), <span class="hljs-number">7</span>);
  assert.<span class="hljs-title function_">strictEqual</span>(sum.<span class="hljs-property">mock</span>.<span class="hljs-title function_">callCount</span>(), <span class="hljs-number">1</span>);

  <span class="hljs-keyword">const</span> call = sum.<span class="hljs-property">mock</span>.<span class="hljs-property">calls</span>[<span class="hljs-number">0</span>];
  assert.<span class="hljs-title function_">deepStrictEqual</span>(call.<span class="hljs-property">arguments</span>, [<span class="hljs-number">3</span>, <span class="hljs-number">4</span>]);
  assert.<span class="hljs-title function_">strictEqual</span>(call.<span class="hljs-property">result</span>, <span class="hljs-number">7</span>);
  assert.<span class="hljs-title function_">strictEqual</span>(call.<span class="hljs-property">error</span>, <span class="hljs-literal">undefined</span>);

  <span class="hljs-comment">// Reset the globally tracked mocks.</span>
  mock.<span class="hljs-title function_">reset</span>();
});</code><code class="language-js cjs"><span class="hljs-meta">'use strict'</span>;
<span class="hljs-keyword">const</span> assert = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:assert'</span>);
<span class="hljs-keyword">const</span> { mock, test } = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:test'</span>);

<span class="hljs-title function_">test</span>(<span class="hljs-string">'spies on a function'</span>, <span class="hljs-function">() =></span> {
  <span class="hljs-keyword">const</span> sum = mock.<span class="hljs-title function_">fn</span>(<span class="hljs-function">(<span class="hljs-params">a, b</span>) =></span> {
    <span class="hljs-keyword">return</span> a + b;
  });

  assert.<span class="hljs-title function_">strictEqual</span>(sum.<span class="hljs-property">mock</span>.<span class="hljs-title function_">callCount</span>(), <span class="hljs-number">0</span>);
  assert.<span class="hljs-title function_">strictEqual</span>(<span class="hljs-title function_">sum</span>(<span class="hljs-number">3</span>, <span class="hljs-number">4</span>), <span class="hljs-number">7</span>);
  assert.<span class="hljs-title function_">strictEqual</span>(sum.<span class="hljs-property">mock</span>.<span class="hljs-title function_">callCount</span>(), <span class="hljs-number">1</span>);

  <span class="hljs-keyword">const</span> call = sum.<span class="hljs-property">mock</span>.<span class="hljs-property">calls</span>[<span class="hljs-number">0</span>];
  assert.<span class="hljs-title function_">deepStrictEqual</span>(call.<span class="hljs-property">arguments</span>, [<span class="hljs-number">3</span>, <span class="hljs-number">4</span>]);
  assert.<span class="hljs-title function_">strictEqual</span>(call.<span class="hljs-property">result</span>, <span class="hljs-number">7</span>);
  assert.<span class="hljs-title function_">strictEqual</span>(call.<span class="hljs-property">error</span>, <span class="hljs-literal">undefined</span>);

  <span class="hljs-comment">// Reset the globally tracked mocks.</span>
  mock.<span class="hljs-title function_">reset</span>();
});</code><button class="copy-button">copy</button></pre>
<p>The same mocking functionality is also exposed on the <a href="#class-testcontext"><code>TestContext</code></a> object
of each test. The following example creates a spy on an object method using the
API exposed on the <code>TestContext</code>. The benefit of mocking via the test context is
that the test runner will automatically restore all mocked functionality once
the test finishes.</p>
<pre><code class="language-js"><span class="hljs-title function_">test</span>(<span class="hljs-string">'spies on an object method'</span>, <span class="hljs-function">(<span class="hljs-params">t</span>) =></span> {
  <span class="hljs-keyword">const</span> number = {
    <span class="hljs-attr">value</span>: <span class="hljs-number">5</span>,
    <span class="hljs-title function_">add</span>(<span class="hljs-params">a</span>) {
      <span class="hljs-keyword">return</span> <span class="hljs-variable language_">this</span>.<span class="hljs-property">value</span> + a;
    },
  };

  t.<span class="hljs-property">mock</span>.<span class="hljs-title function_">method</span>(number, <span class="hljs-string">'add'</span>);
  assert.<span class="hljs-title function_">strictEqual</span>(number.<span class="hljs-property">add</span>.<span class="hljs-property">mock</span>.<span class="hljs-title function_">callCount</span>(), <span class="hljs-number">0</span>);
  assert.<span class="hljs-title function_">strictEqual</span>(number.<span class="hljs-title function_">add</span>(<span class="hljs-number">3</span>), <span class="hljs-number">8</span>);
  assert.<span class="hljs-title function_">strictEqual</span>(number.<span class="hljs-property">add</span>.<span class="hljs-property">mock</span>.<span class="hljs-title function_">callCount</span>(), <span class="hljs-number">1</span>);

  <span class="hljs-keyword">const</span> call = number.<span class="hljs-property">add</span>.<span class="hljs-property">mock</span>.<span class="hljs-property">calls</span>[<span class="hljs-number">0</span>];

  assert.<span class="hljs-title function_">deepStrictEqual</span>(call.<span class="hljs-property">arguments</span>, [<span class="hljs-number">3</span>]);
  assert.<span class="hljs-title function_">strictEqual</span>(call.<span class="hljs-property">result</span>, <span class="hljs-number">8</span>);
  assert.<span class="hljs-title function_">strictEqual</span>(call.<span class="hljs-property">target</span>, <span class="hljs-literal">undefined</span>);
  assert.<span class="hljs-title function_">strictEqual</span>(call.<span class="hljs-property">this</span>, number);
});</code> <button class="copy-button">copy</button></pre>
<h4>Timers<span><a class="mark" href="#timers" id="timers">#</a></span><a aria-hidden="true" class="legacy" id="test_timers"></a></h4>
<p>Mocking timers is a technique commonly used in software testing to simulate and
control the behavior of timers, such as <code>setInterval</code> and <code>setTimeout</code>,
without actually waiting for the specified time intervals.</p>
<p>Refer to the <a href="#class-mocktimers"><code>MockTimers</code></a> class for a full list of methods and features.</p>
<p>This allows developers to write more reliable and
predictable tests for time-dependent functionality.</p>
<p>The example below shows how to mock <code>setTimeout</code>.
Using <code>.enable({ apis: ['setTimeout'] });</code>
it will mock the <code>setTimeout</code> functions in the <a href="./timers.html">node:timers</a> and
<a href="./timers.html#timers-promises-api">node:timers/promises</a> modules,
as well as from the Node.js global context.</p>
<p><strong>Note:</strong> Destructuring functions such as
<code>import { setTimeout } from 'node:timers'</code>
is currently not supported by this API.</p>

<pre class="with-44-chars"><input class="js-flavor-toggle" type="checkbox" checked aria-label="Show modern ES modules syntax"><code class="language-js mjs"><span class="hljs-keyword">import</span> assert <span class="hljs-keyword">from</span> <span class="hljs-string">'node:assert'</span>;
<span class="hljs-keyword">import</span> { mock, test } <span class="hljs-keyword">from</span> <span class="hljs-string">'node:test'</span>;

<span class="hljs-title function_">test</span>(<span class="hljs-string">'mocks setTimeout to be executed synchronously without having to actually wait for it'</span>, <span class="hljs-function">() =></span> {
  <span class="hljs-keyword">const</span> fn = mock.<span class="hljs-title function_">fn</span>();

  <span class="hljs-comment">// Optionally choose what to mock</span>
  mock.<span class="hljs-property">timers</span>.<span class="hljs-title function_">enable</span>({ <span class="hljs-attr">apis</span>: [<span class="hljs-string">'setTimeout'</span>] });
  <span class="hljs-built_in">setTimeout</span>(fn, <span class="hljs-number">9999</span>);
  assert.<span class="hljs-title function_">strictEqual</span>(fn.<span class="hljs-property">mock</span>.<span class="hljs-title function_">callCount</span>(), <span class="hljs-number">0</span>);

  <span class="hljs-comment">// Advance in time</span>
  mock.<span class="hljs-property">timers</span>.<span class="hljs-title function_">tick</span>(<span class="hljs-number">9999</span>);
  assert.<span class="hljs-title function_">strictEqual</span>(fn.<span class="hljs-property">mock</span>.<span class="hljs-title function_">callCount</span>(), <span class="hljs-number">1</span>);

  <span class="hljs-comment">// Reset the globally tracked mocks.</span>
  mock.<span class="hljs-property">timers</span>.<span class="hljs-title function_">reset</span>();

  <span class="hljs-comment">// If you call reset mock instance, it will also reset timers instance</span>
  mock.<span class="hljs-title function_">reset</span>();
});</code><code class="language-js cjs"><span class="hljs-keyword">const</span> assert = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:assert'</span>);
<span class="hljs-keyword">const</span> { mock, test } = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:test'</span>);

<span class="hljs-title function_">test</span>(<span class="hljs-string">'mocks setTimeout to be executed synchronously without having to actually wait for it'</span>, <span class="hljs-function">() =></span> {
  <span class="hljs-keyword">const</span> fn = mock.<span class="hljs-title function_">fn</span>();

  <span class="hljs-comment">// Optionally choose what to mock</span>
  mock.<span class="hljs-property">timers</span>.<span class="hljs-title function_">enable</span>({ <span class="hljs-attr">apis</span>: [<span class="hljs-string">'setTimeout'</span>] });
  <span class="hljs-built_in">setTimeout</span>(fn, <span class="hljs-number">9999</span>);
  assert.<span class="hljs-title function_">strictEqual</span>(fn.<span class="hljs-property">mock</span>.<span class="hljs-title function_">callCount</span>(), <span class="hljs-number">0</span>);

  <span class="hljs-comment">// Advance in time</span>
  mock.<span class="hljs-property">timers</span>.<span class="hljs-title function_">tick</span>(<span class="hljs-number">9999</span>);
  assert.<span class="hljs-title function_">strictEqual</span>(fn.<span class="hljs-property">mock</span>.<span class="hljs-title function_">callCount</span>(), <span class="hljs-number">1</span>);

  <span class="hljs-comment">// Reset the globally tracked mocks.</span>
  mock.<span class="hljs-property">timers</span>.<span class="hljs-title function_">reset</span>();

  <span class="hljs-comment">// If you call reset mock instance, it will also reset timers instance</span>
  mock.<span class="hljs-title function_">reset</span>();
});</code><button class="copy-button">copy</button></pre>
<p>The same mocking functionality is also exposed in the mock property on the <a href="#class-testcontext"><code>TestContext</code></a> object
of each test. The benefit of mocking via the test context is
that the test runner will automatically restore all mocked timers
functionality once the test finishes.</p>

<pre class="with-38-chars"><input class="js-flavor-toggle" type="checkbox" checked aria-label="Show modern ES modules syntax"><code class="language-js mjs"><span class="hljs-keyword">import</span> assert <span class="hljs-keyword">from</span> <span class="hljs-string">'node:assert'</span>;
<span class="hljs-keyword">import</span> { test } <span class="hljs-keyword">from</span> <span class="hljs-string">'node:test'</span>;

<span class="hljs-title function_">test</span>(<span class="hljs-string">'mocks setTimeout to be executed synchronously without having to actually wait for it'</span>, <span class="hljs-function">(<span class="hljs-params">context</span>) =></span> {
  <span class="hljs-keyword">const</span> fn = context.<span class="hljs-property">mock</span>.<span class="hljs-title function_">fn</span>();

  <span class="hljs-comment">// Optionally choose what to mock</span>
  context.<span class="hljs-property">mock</span>.<span class="hljs-property">timers</span>.<span class="hljs-title function_">enable</span>({ <span class="hljs-attr">apis</span>: [<span class="hljs-string">'setTimeout'</span>] });
  <span class="hljs-built_in">setTimeout</span>(fn, <span class="hljs-number">9999</span>);
  assert.<span class="hljs-title function_">strictEqual</span>(fn.<span class="hljs-property">mock</span>.<span class="hljs-title function_">callCount</span>(), <span class="hljs-number">0</span>);

  <span class="hljs-comment">// Advance in time</span>
  context.<span class="hljs-property">mock</span>.<span class="hljs-property">timers</span>.<span class="hljs-title function_">tick</span>(<span class="hljs-number">9999</span>);
  assert.<span class="hljs-title function_">strictEqual</span>(fn.<span class="hljs-property">mock</span>.<span class="hljs-title function_">callCount</span>(), <span class="hljs-number">1</span>);
});</code><code class="language-js cjs"><span class="hljs-keyword">const</span> assert = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:assert'</span>);
<span class="hljs-keyword">const</span> { test } = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:test'</span>);

<span class="hljs-title function_">test</span>(<span class="hljs-string">'mocks setTimeout to be executed synchronously without having to actually wait for it'</span>, <span class="hljs-function">(<span class="hljs-params">context</span>) =></span> {
  <span class="hljs-keyword">const</span> fn = context.<span class="hljs-property">mock</span>.<span class="hljs-title function_">fn</span>();

  <span class="hljs-comment">// Optionally choose what to mock</span>
  context.<span class="hljs-property">mock</span>.<span class="hljs-property">timers</span>.<span class="hljs-title function_">enable</span>({ <span class="hljs-attr">apis</span>: [<span class="hljs-string">'setTimeout'</span>] });
  <span class="hljs-built_in">setTimeout</span>(fn, <span class="hljs-number">9999</span>);
  assert.<span class="hljs-title function_">strictEqual</span>(fn.<span class="hljs-property">mock</span>.<span class="hljs-title function_">callCount</span>(), <span class="hljs-number">0</span>);

  <span class="hljs-comment">// Advance in time</span>
  context.<span class="hljs-property">mock</span>.<span class="hljs-property">timers</span>.<span class="hljs-title function_">tick</span>(<span class="hljs-number">9999</span>);
  assert.<span class="hljs-title function_">strictEqual</span>(fn.<span class="hljs-property">mock</span>.<span class="hljs-title function_">callCount</span>(), <span class="hljs-number">1</span>);
});</code><button class="copy-button">copy</button></pre>
<h4>Dates<span><a class="mark" href="#dates" id="dates">#</a></span><a aria-hidden="true" class="legacy" id="test_dates"></a></h4>
<p>The mock timers API also allows the mocking of the <code>Date</code> object. This is a
useful feature for testing time-dependent functionality, or to simulate
internal calendar functions such as <code>Date.now()</code>.</p>
<p>The dates implementation is also part of the <a href="#class-mocktimers"><code>MockTimers</code></a> class. Refer to it
for a full list of methods and features.</p>
<p><strong>Note:</strong> Dates and timers are dependent when mocked together. This means that
if you have both the <code>Date</code> and <code>setTimeout</code> mocked, advancing the time will
also advance the mocked date as they simulate a single internal clock.</p>
<p>The example below show how to mock the <code>Date</code> object and obtain the current
<code>Date.now()</code> value.</p>

<pre class="with-38-chars"><input class="js-flavor-toggle" type="checkbox" checked aria-label="Show modern ES modules syntax"><code class="language-js mjs"><span class="hljs-keyword">import</span> assert <span class="hljs-keyword">from</span> <span class="hljs-string">'node:assert'</span>;
<span class="hljs-keyword">import</span> { test } <span class="hljs-keyword">from</span> <span class="hljs-string">'node:test'</span>;

<span class="hljs-title function_">test</span>(<span class="hljs-string">'mocks the Date object'</span>, <span class="hljs-function">(<span class="hljs-params">context</span>) =></span> {
  <span class="hljs-comment">// Optionally choose what to mock</span>
  context.<span class="hljs-property">mock</span>.<span class="hljs-property">timers</span>.<span class="hljs-title function_">enable</span>({ <span class="hljs-attr">apis</span>: [<span class="hljs-string">'Date'</span>] });
  <span class="hljs-comment">// If not specified, the initial date will be based on 0 in the UNIX epoch</span>
  assert.<span class="hljs-title function_">strictEqual</span>(<span class="hljs-title class_">Date</span>.<span class="hljs-title function_">now</span>(), <span class="hljs-number">0</span>);

  <span class="hljs-comment">// Advance in time will also advance the date</span>
  context.<span class="hljs-property">mock</span>.<span class="hljs-property">timers</span>.<span class="hljs-title function_">tick</span>(<span class="hljs-number">9999</span>);
  assert.<span class="hljs-title function_">strictEqual</span>(<span class="hljs-title class_">Date</span>.<span class="hljs-title function_">now</span>(), <span class="hljs-number">9999</span>);
});</code><code class="language-js cjs"><span class="hljs-keyword">const</span> assert = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:assert'</span>);
<span class="hljs-keyword">const</span> { test } = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:test'</span>);

<span class="hljs-title function_">test</span>(<span class="hljs-string">'mocks the Date object'</span>, <span class="hljs-function">(<span class="hljs-params">context</span>) =></span> {
  <span class="hljs-comment">// Optionally choose what to mock</span>
  context.<span class="hljs-property">mock</span>.<span class="hljs-property">timers</span>.<span class="hljs-title function_">enable</span>({ <span class="hljs-attr">apis</span>: [<span class="hljs-string">'Date'</span>] });
  <span class="hljs-comment">// If not specified, the initial date will be based on 0 in the UNIX epoch</span>
  assert.<span class="hljs-title function_">strictEqual</span>(<span class="hljs-title class_">Date</span>.<span class="hljs-title function_">now</span>(), <span class="hljs-number">0</span>);

  <span class="hljs-comment">// Advance in time will also advance the date</span>
  context.<span class="hljs-property">mock</span>.<span class="hljs-property">timers</span>.<span class="hljs-title function_">tick</span>(<span class="hljs-number">9999</span>);
  assert.<span class="hljs-title function_">strictEqual</span>(<span class="hljs-title class_">Date</span>.<span class="hljs-title function_">now</span>(), <span class="hljs-number">9999</span>);
});</code><button class="copy-button">copy</button></pre>
<p>If there is no initial epoch set, the initial date will be based on 0 in the
Unix epoch. This is January 1st, 1970, 00:00:00 UTC. You can set an initial date
by passing a <code>now</code> property to the <code>.enable()</code> method. This value will be used
as the initial date for the mocked <code>Date</code> object. It can either be a positive
integer, or another Date object.</p>

<pre class="with-38-chars"><input class="js-flavor-toggle" type="checkbox" checked aria-label="Show modern ES modules syntax"><code class="language-js mjs"><span class="hljs-keyword">import</span> assert <span class="hljs-keyword">from</span> <span class="hljs-string">'node:assert'</span>;
<span class="hljs-keyword">import</span> { test } <span class="hljs-keyword">from</span> <span class="hljs-string">'node:test'</span>;

<span class="hljs-title function_">test</span>(<span class="hljs-string">'mocks the Date object with initial time'</span>, <span class="hljs-function">(<span class="hljs-params">context</span>) =></span> {
  <span class="hljs-comment">// Optionally choose what to mock</span>
  context.<span class="hljs-property">mock</span>.<span class="hljs-property">timers</span>.<span class="hljs-title function_">enable</span>({ <span class="hljs-attr">apis</span>: [<span class="hljs-string">'Date'</span>], <span class="hljs-attr">now</span>: <span class="hljs-number">100</span> });
  assert.<span class="hljs-title function_">strictEqual</span>(<span class="hljs-title class_">Date</span>.<span class="hljs-title function_">now</span>(), <span class="hljs-number">100</span>);

  <span class="hljs-comment">// Advance in time will also advance the date</span>
  context.<span class="hljs-property">mock</span>.<span class="hljs-property">timers</span>.<span class="hljs-title function_">tick</span>(<span class="hljs-number">200</span>);
  assert.<span class="hljs-title function_">strictEqual</span>(<span class="hljs-title class_">Date</span>.<span class="hljs-title function_">now</span>(), <span class="hljs-number">300</span>);
});</code><code class="language-js cjs"><span class="hljs-keyword">const</span> assert = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:assert'</span>);
<span class="hljs-keyword">const</span> { test } = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:test'</span>);

<span class="hljs-title function_">test</span>(<span class="hljs-string">'mocks the Date object with initial time'</span>, <span class="hljs-function">(<span class="hljs-params">context</span>) =></span> {
  <span class="hljs-comment">// Optionally choose what to mock</span>
  context.<span class="hljs-property">mock</span>.<span class="hljs-property">timers</span>.<span class="hljs-title function_">enable</span>({ <span class="hljs-attr">apis</span>: [<span class="hljs-string">'Date'</span>], <span class="hljs-attr">now</span>: <span class="hljs-number">100</span> });
  assert.<span class="hljs-title function_">strictEqual</span>(<span class="hljs-title class_">Date</span>.<span class="hljs-title function_">now</span>(), <span class="hljs-number">100</span>);

  <span class="hljs-comment">// Advance in time will also advance the date</span>
  context.<span class="hljs-property">mock</span>.<span class="hljs-property">timers</span>.<span class="hljs-title function_">tick</span>(<span class="hljs-number">200</span>);
  assert.<span class="hljs-title function_">strictEqual</span>(<span class="hljs-title class_">Date</span>.<span class="hljs-title function_">now</span>(), <span class="hljs-number">300</span>);
});</code><button class="copy-button">copy</button></pre>
<p>You can use the <code>.setTime()</code> method to manually move the mocked date to another
time. This method only accepts a positive integer.</p>
<p><strong>Note:</strong> This method will execute any mocked timers that are in the past
from the new time.</p>
<p>In the below example we are setting a new time for the mocked date.</p>

<pre class="with-38-chars"><input class="js-flavor-toggle" type="checkbox" checked aria-label="Show modern ES modules syntax"><code class="language-js mjs"><span class="hljs-keyword">import</span> assert <span class="hljs-keyword">from</span> <span class="hljs-string">'node:assert'</span>;
<span class="hljs-keyword">import</span> { test } <span class="hljs-keyword">from</span> <span class="hljs-string">'node:test'</span>;

<span class="hljs-title function_">test</span>(<span class="hljs-string">'sets the time of a date object'</span>, <span class="hljs-function">(<span class="hljs-params">context</span>) =></span> {
  <span class="hljs-comment">// Optionally choose what to mock</span>
  context.<span class="hljs-property">mock</span>.<span class="hljs-property">timers</span>.<span class="hljs-title function_">enable</span>({ <span class="hljs-attr">apis</span>: [<span class="hljs-string">'Date'</span>], <span class="hljs-attr">now</span>: <span class="hljs-number">100</span> });
  assert.<span class="hljs-title function_">strictEqual</span>(<span class="hljs-title class_">Date</span>.<span class="hljs-title function_">now</span>(), <span class="hljs-number">100</span>);

  <span class="hljs-comment">// Advance in time will also advance the date</span>
  context.<span class="hljs-property">mock</span>.<span class="hljs-property">timers</span>.<span class="hljs-title function_">setTime</span>(<span class="hljs-number">1000</span>);
  context.<span class="hljs-property">mock</span>.<span class="hljs-property">timers</span>.<span class="hljs-title function_">tick</span>(<span class="hljs-number">200</span>);
  assert.<span class="hljs-title function_">strictEqual</span>(<span class="hljs-title class_">Date</span>.<span class="hljs-title function_">now</span>(), <span class="hljs-number">1200</span>);
});</code><code class="language-js cjs"><span class="hljs-keyword">const</span> assert = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:assert'</span>);
<span class="hljs-keyword">const</span> { test } = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:test'</span>);

<span class="hljs-title function_">test</span>(<span class="hljs-string">'sets the time of a date object'</span>, <span class="hljs-function">(<span class="hljs-params">context</span>) =></span> {
  <span class="hljs-comment">// Optionally choose what to mock</span>
  context.<span class="hljs-property">mock</span>.<span class="hljs-property">timers</span>.<span class="hljs-title function_">enable</span>({ <span class="hljs-attr">apis</span>: [<span class="hljs-string">'Date'</span>], <span class="hljs-attr">now</span>: <span class="hljs-number">100</span> });
  assert.<span class="hljs-title function_">strictEqual</span>(<span class="hljs-title class_">Date</span>.<span class="hljs-title function_">now</span>(), <span class="hljs-number">100</span>);

  <span class="hljs-comment">// Advance in time will also advance the date</span>
  context.<span class="hljs-property">mock</span>.<span class="hljs-property">timers</span>.<span class="hljs-title function_">setTime</span>(<span class="hljs-number">1000</span>);
  context.<span class="hljs-property">mock</span>.<span class="hljs-property">timers</span>.<span class="hljs-title function_">tick</span>(<span class="hljs-number">200</span>);
  assert.<span class="hljs-title function_">strictEqual</span>(<span class="hljs-title class_">Date</span>.<span class="hljs-title function_">now</span>(), <span class="hljs-number">1200</span>);
});</code><button class="copy-button">copy</button></pre>
<p>If you have any timer that's set to run in the past, it will be executed as if
the <code>.tick()</code> method has been called. This is useful if you want to test
time-dependent functionality that's already in the past.</p>

<pre class="with-38-chars"><input class="js-flavor-toggle" type="checkbox" checked aria-label="Show modern ES modules syntax"><code class="language-js mjs"><span class="hljs-keyword">import</span> assert <span class="hljs-keyword">from</span> <span class="hljs-string">'node:assert'</span>;
<span class="hljs-keyword">import</span> { test } <span class="hljs-keyword">from</span> <span class="hljs-string">'node:test'</span>;

<span class="hljs-title function_">test</span>(<span class="hljs-string">'runs timers as setTime passes ticks'</span>, <span class="hljs-function">(<span class="hljs-params">context</span>) =></span> {
  <span class="hljs-comment">// Optionally choose what to mock</span>
  context.<span class="hljs-property">mock</span>.<span class="hljs-property">timers</span>.<span class="hljs-title function_">enable</span>({ <span class="hljs-attr">apis</span>: [<span class="hljs-string">'setTimeout'</span>, <span class="hljs-string">'Date'</span>] });
  <span class="hljs-keyword">const</span> fn = context.<span class="hljs-property">mock</span>.<span class="hljs-title function_">fn</span>();
  <span class="hljs-built_in">setTimeout</span>(fn, <span class="hljs-number">1000</span>);

  context.<span class="hljs-property">mock</span>.<span class="hljs-property">timers</span>.<span class="hljs-title function_">setTime</span>(<span class="hljs-number">800</span>);
  <span class="hljs-comment">// Timer is not executed as the time is not yet reached</span>
  assert.<span class="hljs-title function_">strictEqual</span>(fn.<span class="hljs-property">mock</span>.<span class="hljs-title function_">callCount</span>(), <span class="hljs-number">0</span>);
  assert.<span class="hljs-title function_">strictEqual</span>(<span class="hljs-title class_">Date</span>.<span class="hljs-title function_">now</span>(), <span class="hljs-number">800</span>);

  context.<span class="hljs-property">mock</span>.<span class="hljs-property">timers</span>.<span class="hljs-title function_">setTime</span>(<span class="hljs-number">1200</span>);
  <span class="hljs-comment">// Timer is executed as the time is now reached</span>
  assert.<span class="hljs-title function_">strictEqual</span>(fn.<span class="hljs-property">mock</span>.<span class="hljs-title function_">callCount</span>(), <span class="hljs-number">1</span>);
  assert.<span class="hljs-title function_">strictEqual</span>(<span class="hljs-title class_">Date</span>.<span class="hljs-title function_">now</span>(), <span class="hljs-number">1200</span>);
});</code><code class="language-js cjs"><span class="hljs-keyword">const</span> assert = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:assert'</span>);
<span class="hljs-keyword">const</span> { test } = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:test'</span>);

<span class="hljs-title function_">test</span>(<span class="hljs-string">'runs timers as setTime passes ticks'</span>, <span class="hljs-function">(<span class="hljs-params">context</span>) =></span> {
  <span class="hljs-comment">// Optionally choose what to mock</span>
  context.<span class="hljs-property">mock</span>.<span class="hljs-property">timers</span>.<span class="hljs-title function_">enable</span>({ <span class="hljs-attr">apis</span>: [<span class="hljs-string">'setTimeout'</span>, <span class="hljs-string">'Date'</span>] });
  <span class="hljs-keyword">const</span> fn = context.<span class="hljs-property">mock</span>.<span class="hljs-title function_">fn</span>();
  <span class="hljs-built_in">setTimeout</span>(fn, <span class="hljs-number">1000</span>);

  context.<span class="hljs-property">mock</span>.<span class="hljs-property">timers</span>.<span class="hljs-title function_">setTime</span>(<span class="hljs-number">800</span>);
  <span class="hljs-comment">// Timer is not executed as the time is not yet reached</span>
  assert.<span class="hljs-title function_">strictEqual</span>(fn.<span class="hljs-property">mock</span>.<span class="hljs-title function_">callCount</span>(), <span class="hljs-number">0</span>);
  assert.<span class="hljs-title function_">strictEqual</span>(<span class="hljs-title class_">Date</span>.<span class="hljs-title function_">now</span>(), <span class="hljs-number">800</span>);

  context.<span class="hljs-property">mock</span>.<span class="hljs-property">timers</span>.<span class="hljs-title function_">setTime</span>(<span class="hljs-number">1200</span>);
  <span class="hljs-comment">// Timer is executed as the time is now reached</span>
  assert.<span class="hljs-title function_">strictEqual</span>(fn.<span class="hljs-property">mock</span>.<span class="hljs-title function_">callCount</span>(), <span class="hljs-number">1</span>);
  assert.<span class="hljs-title function_">strictEqual</span>(<span class="hljs-title class_">Date</span>.<span class="hljs-title function_">now</span>(), <span class="hljs-number">1200</span>);
});</code><button class="copy-button">copy</button></pre>
<p>Using <code>.runAll()</code> will execute all timers that are currently in the queue. This
will also advance the mocked date to the time of the last timer that was
executed as if the time has passed.</p>

<pre class="with-38-chars"><input class="js-flavor-toggle" type="checkbox" checked aria-label="Show modern ES modules syntax"><code class="language-js mjs"><span class="hljs-keyword">import</span> assert <span class="hljs-keyword">from</span> <span class="hljs-string">'node:assert'</span>;
<span class="hljs-keyword">import</span> { test } <span class="hljs-keyword">from</span> <span class="hljs-string">'node:test'</span>;

<span class="hljs-title function_">test</span>(<span class="hljs-string">'runs timers as setTime passes ticks'</span>, <span class="hljs-function">(<span class="hljs-params">context</span>) =></span> {
  <span class="hljs-comment">// Optionally choose what to mock</span>
  context.<span class="hljs-property">mock</span>.<span class="hljs-property">timers</span>.<span class="hljs-title function_">enable</span>({ <span class="hljs-attr">apis</span>: [<span class="hljs-string">'setTimeout'</span>, <span class="hljs-string">'Date'</span>] });
  <span class="hljs-keyword">const</span> fn = context.<span class="hljs-property">mock</span>.<span class="hljs-title function_">fn</span>();
  <span class="hljs-built_in">setTimeout</span>(fn, <span class="hljs-number">1000</span>);
  <span class="hljs-built_in">setTimeout</span>(fn, <span class="hljs-number">2000</span>);
  <span class="hljs-built_in">setTimeout</span>(fn, <span class="hljs-number">3000</span>);

  context.<span class="hljs-property">mock</span>.<span class="hljs-property">timers</span>.<span class="hljs-title function_">runAll</span>();
  <span class="hljs-comment">// All timers are executed as the time is now reached</span>
  assert.<span class="hljs-title function_">strictEqual</span>(fn.<span class="hljs-property">mock</span>.<span class="hljs-title function_">callCount</span>(), <span class="hljs-number">3</span>);
  assert.<span class="hljs-title function_">strictEqual</span>(<span class="hljs-title class_">Date</span>.<span class="hljs-title function_">now</span>(), <span class="hljs-number">3000</span>);
});</code><code class="language-js cjs"><span class="hljs-keyword">const</span> assert = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:assert'</span>);
<span class="hljs-keyword">const</span> { test } = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:test'</span>);

<span class="hljs-title function_">test</span>(<span class="hljs-string">'runs timers as setTime passes ticks'</span>, <span class="hljs-function">(<span class="hljs-params">context</span>) =></span> {
  <span class="hljs-comment">// Optionally choose what to mock</span>
  context.<span class="hljs-property">mock</span>.<span class="hljs-property">timers</span>.<span class="hljs-title function_">enable</span>({ <span class="hljs-attr">apis</span>: [<span class="hljs-string">'setTimeout'</span>, <span class="hljs-string">'Date'</span>] });
  <span class="hljs-keyword">const</span> fn = context.<span class="hljs-property">mock</span>.<span class="hljs-title function_">fn</span>();
  <span class="hljs-built_in">setTimeout</span>(fn, <span class="hljs-number">1000</span>);
  <span class="hljs-built_in">setTimeout</span>(fn, <span class="hljs-number">2000</span>);
  <span class="hljs-built_in">setTimeout</span>(fn, <span class="hljs-number">3000</span>);

  context.<span class="hljs-property">mock</span>.<span class="hljs-property">timers</span>.<span class="hljs-title function_">runAll</span>();
  <span class="hljs-comment">// All timers are executed as the time is now reached</span>
  assert.<span class="hljs-title function_">strictEqual</span>(fn.<span class="hljs-property">mock</span>.<span class="hljs-title function_">callCount</span>(), <span class="hljs-number">3</span>);
  assert.<span class="hljs-title function_">strictEqual</span>(<span class="hljs-title class_">Date</span>.<span class="hljs-title function_">now</span>(), <span class="hljs-number">3000</span>);
});</code><button class="copy-button">copy</button></pre>
</section><section><h3>Snapshot testing<span><a class="mark" href="#snapshot-testing" id="snapshot-testing">#</a></span><a aria-hidden="true" class="legacy" id="test_snapshot_testing"></a></h3>
<div class="api_metadata">
<details class="changelog"><summary>History</summary>
<table>
<tbody><tr><th>Version</th><th>Changes</th></tr>
<tr><td>v23.4.0</td>
<td><p>Snapsnot testing is no longer experimental.</p></td></tr>
<tr><td>v22.3.0</td>
<td><p><span>Added in: v22.3.0</span></p></td></tr>
</tbody></table>
</details>
</div>
<p>Snapshot tests allow arbitrary values to be serialized into string values and
compared against a set of known good values. The known good values are known as
snapshots, and are stored in a snapshot file. Snapshot files are managed by the
test runner, but are designed to be human readable to aid in debugging. Best
practice is for snapshot files to be checked into source control along with your
test files.</p>
<p>Snapshot files are generated by starting Node.js with the
<a href="cli.html#--test-update-snapshots"><code>--test-update-snapshots</code></a> command-line flag. A separate snapshot file is
generated for each test file. By default, the snapshot file has the same name
as the test file with a <code>.snapshot</code> file extension. This behavior can be
configured using the <code>snapshot.setResolveSnapshotPath()</code> function. Each
snapshot assertion corresponds to an export in the snapshot file.</p>
<p>An example snapshot test is shown below. The first time this test is executed,
it will fail because the corresponding snapshot file does not exist.</p>
<pre><code class="language-js"><span class="hljs-comment">// test.js</span>
<span class="hljs-title function_">suite</span>(<span class="hljs-string">'suite of snapshot tests'</span>, <span class="hljs-function">() =></span> {
  <span class="hljs-title function_">test</span>(<span class="hljs-string">'snapshot test'</span>, <span class="hljs-function">(<span class="hljs-params">t</span>) =></span> {
    t.<span class="hljs-property">assert</span>.<span class="hljs-title function_">snapshot</span>({ <span class="hljs-attr">value1</span>: <span class="hljs-number">1</span>, <span class="hljs-attr">value2</span>: <span class="hljs-number">2</span> });
    t.<span class="hljs-property">assert</span>.<span class="hljs-title function_">snapshot</span>(<span class="hljs-number">5</span>);
  });
});</code> <button class="copy-button">copy</button></pre>
<p>Generate the snapshot file by running the test file with
<code>--test-update-snapshots</code>. The test should pass, and a file named
<code>test.js.snapshot</code> is created in the same directory as the test file. The
contents of the snapshot file are shown below. Each snapshot is identified by
the full name of test and a counter to differentiate between snapshots in the
same test.</p>
<pre><code class="language-js"><span class="hljs-built_in">exports</span>[<span class="hljs-string">`suite of snapshot tests > snapshot test 1`</span>] = <span class="hljs-string">`
{
  "value1": 1,
  "value2": 2
}
`</span>;

<span class="hljs-built_in">exports</span>[<span class="hljs-string">`suite of snapshot tests > snapshot test 2`</span>] = <span class="hljs-string">`
5
`</span>;</code> <button class="copy-button">copy</button></pre>
<p>Once the snapshot file is created, run the tests again without the
<code>--test-update-snapshots</code> flag. The tests should pass now.</p>
</section><section><h3>Test reporters<span><a class="mark" href="#test-reporters" id="test-reporters">#</a></span><a aria-hidden="true" class="legacy" id="test_test_reporters"></a></h3>
<div class="api_metadata">
<details class="changelog"><summary>History</summary>
<table>
<tbody><tr><th>Version</th><th>Changes</th></tr>
<tr><td>v19.9.0, v18.17.0</td>
<td><p>Reporters are now exposed at <code>node:test/reporters</code>.</p></td></tr>
<tr><td>v19.6.0, v18.15.0</td>
<td><p><span>Added in: v19.6.0, v18.15.0</span></p></td></tr>
</tbody></table>
</details>
</div>
<p>The <code>node:test</code> module supports passing <a href="cli.html#--test-reporter"><code>--test-reporter</code></a>
flags for the test runner to use a specific reporter.</p>
<p>The following built-reporters are supported:</p>
<ul>
<li>
<p><code>tap</code>
The <code>tap</code> reporter outputs the test results in the <a href="https://testanything.org/">TAP</a> format.</p>
</li>
<li>
<p><code>spec</code>
The <code>spec</code> reporter outputs the test results in a human-readable format.</p>
</li>
<li>
<p><code>dot</code>
The <code>dot</code> reporter outputs the test results in a compact format,
where each passing test is represented by a <code>.</code>,
and each failing test is represented by a <code>X</code>.</p>
</li>
<li>
<p><code>junit</code>
The junit reporter outputs test results in a jUnit XML format</p>
</li>
<li>
<p><code>lcov</code>
The <code>lcov</code> reporter outputs test coverage when used with the
<a href="cli.html#--experimental-test-coverage"><code>--experimental-test-coverage</code></a> flag.</p>
</li>
</ul>
<p>When <code>stdout</code> is a <a href="tty.html">TTY</a>, the <code>spec</code> reporter is used by default.
Otherwise, the <code>tap</code> reporter is used by default.</p>
<p>The exact output of these reporters is subject to change between versions of
Node.js, and should not be relied on programmatically. If programmatic access
to the test runner's output is required, use the events emitted by the
<a href="test.html#class-testsstream" class="type">&#x3C;TestsStream></a>.</p>
<p>The reporters are available via the <code>node:test/reporters</code> module:</p>

<pre class="with-71-chars"><input class="js-flavor-toggle" type="checkbox" checked aria-label="Show modern ES modules syntax"><code class="language-js mjs"><span class="hljs-keyword">import</span> { tap, spec, dot, junit, lcov } <span class="hljs-keyword">from</span> <span class="hljs-string">'node:test/reporters'</span>;</code><code class="language-js cjs"><span class="hljs-keyword">const</span> { tap, spec, dot, junit, lcov } = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:test/reporters'</span>);</code><button class="copy-button">copy</button></pre>
<h4>Custom reporters<span><a class="mark" href="#custom-reporters" id="custom-reporters">#</a></span><a aria-hidden="true" class="legacy" id="test_custom_reporters"></a></h4>
<p><a href="cli.html#--test-reporter"><code>--test-reporter</code></a> can be used to specify a path to custom reporter.
A custom reporter is a module that exports a value
accepted by <a href="stream.html#streamcomposestreams">stream.compose</a>.
Reporters should transform events emitted by a <a href="test.html#class-testsstream" class="type">&#x3C;TestsStream></a></p>
<p>Example of a custom reporter using <a href="stream.html#class-streamtransform" class="type">&#x3C;stream.Transform></a>:</p>

<pre class="with-45-chars"><input class="js-flavor-toggle" type="checkbox" checked aria-label="Show modern ES modules syntax"><code class="language-js mjs"><span class="hljs-keyword">import</span> { <span class="hljs-title class_">Transform</span> } <span class="hljs-keyword">from</span> <span class="hljs-string">'node:stream'</span>;

<span class="hljs-keyword">const</span> customReporter = <span class="hljs-keyword">new</span> <span class="hljs-title class_">Transform</span>({
  <span class="hljs-attr">writableObjectMode</span>: <span class="hljs-literal">true</span>,
  <span class="hljs-title function_">transform</span>(<span class="hljs-params">event, encoding, callback</span>) {
    <span class="hljs-keyword">switch</span> (event.<span class="hljs-property">type</span>) {
      <span class="hljs-keyword">case</span> <span class="hljs-string">'test:dequeue'</span>:
        <span class="hljs-title function_">callback</span>(<span class="hljs-literal">null</span>, <span class="hljs-string">`test <span class="hljs-subst">${event.data.name}</span> dequeued`</span>);
        <span class="hljs-keyword">break</span>;
      <span class="hljs-keyword">case</span> <span class="hljs-string">'test:enqueue'</span>:
        <span class="hljs-title function_">callback</span>(<span class="hljs-literal">null</span>, <span class="hljs-string">`test <span class="hljs-subst">${event.data.name}</span> enqueued`</span>);
        <span class="hljs-keyword">break</span>;
      <span class="hljs-keyword">case</span> <span class="hljs-string">'test:watch:drained'</span>:
        <span class="hljs-title function_">callback</span>(<span class="hljs-literal">null</span>, <span class="hljs-string">'test watch queue drained'</span>);
        <span class="hljs-keyword">break</span>;
      <span class="hljs-keyword">case</span> <span class="hljs-string">'test:start'</span>:
        <span class="hljs-title function_">callback</span>(<span class="hljs-literal">null</span>, <span class="hljs-string">`test <span class="hljs-subst">${event.data.name}</span> started`</span>);
        <span class="hljs-keyword">break</span>;
      <span class="hljs-keyword">case</span> <span class="hljs-string">'test:pass'</span>:
        <span class="hljs-title function_">callback</span>(<span class="hljs-literal">null</span>, <span class="hljs-string">`test <span class="hljs-subst">${event.data.name}</span> passed`</span>);
        <span class="hljs-keyword">break</span>;
      <span class="hljs-keyword">case</span> <span class="hljs-string">'test:fail'</span>:
        <span class="hljs-title function_">callback</span>(<span class="hljs-literal">null</span>, <span class="hljs-string">`test <span class="hljs-subst">${event.data.name}</span> failed`</span>);
        <span class="hljs-keyword">break</span>;
      <span class="hljs-keyword">case</span> <span class="hljs-string">'test:plan'</span>:
        <span class="hljs-title function_">callback</span>(<span class="hljs-literal">null</span>, <span class="hljs-string">'test plan'</span>);
        <span class="hljs-keyword">break</span>;
      <span class="hljs-keyword">case</span> <span class="hljs-string">'test:diagnostic'</span>:
      <span class="hljs-keyword">case</span> <span class="hljs-string">'test:stderr'</span>:
      <span class="hljs-keyword">case</span> <span class="hljs-string">'test:stdout'</span>:
        <span class="hljs-title function_">callback</span>(<span class="hljs-literal">null</span>, event.<span class="hljs-property">data</span>.<span class="hljs-property">message</span>);
        <span class="hljs-keyword">break</span>;
      <span class="hljs-keyword">case</span> <span class="hljs-string">'test:coverage'</span>: {
        <span class="hljs-keyword">const</span> { totalLineCount } = event.<span class="hljs-property">data</span>.<span class="hljs-property">summary</span>.<span class="hljs-property">totals</span>;
        <span class="hljs-title function_">callback</span>(<span class="hljs-literal">null</span>, <span class="hljs-string">`total line count: <span class="hljs-subst">${totalLineCount}</span>\n`</span>);
        <span class="hljs-keyword">break</span>;
      }
    }
  },
});

<span class="hljs-keyword">export</span> <span class="hljs-keyword">default</span> customReporter;</code><code class="language-js cjs"><span class="hljs-keyword">const</span> { <span class="hljs-title class_">Transform</span> } = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:stream'</span>);

<span class="hljs-keyword">const</span> customReporter = <span class="hljs-keyword">new</span> <span class="hljs-title class_">Transform</span>({
  <span class="hljs-attr">writableObjectMode</span>: <span class="hljs-literal">true</span>,
  <span class="hljs-title function_">transform</span>(<span class="hljs-params">event, encoding, callback</span>) {
    <span class="hljs-keyword">switch</span> (event.<span class="hljs-property">type</span>) {
      <span class="hljs-keyword">case</span> <span class="hljs-string">'test:dequeue'</span>:
        <span class="hljs-title function_">callback</span>(<span class="hljs-literal">null</span>, <span class="hljs-string">`test <span class="hljs-subst">${event.data.name}</span> dequeued`</span>);
        <span class="hljs-keyword">break</span>;
      <span class="hljs-keyword">case</span> <span class="hljs-string">'test:enqueue'</span>:
        <span class="hljs-title function_">callback</span>(<span class="hljs-literal">null</span>, <span class="hljs-string">`test <span class="hljs-subst">${event.data.name}</span> enqueued`</span>);
        <span class="hljs-keyword">break</span>;
      <span class="hljs-keyword">case</span> <span class="hljs-string">'test:watch:drained'</span>:
        <span class="hljs-title function_">callback</span>(<span class="hljs-literal">null</span>, <span class="hljs-string">'test watch queue drained'</span>);
        <span class="hljs-keyword">break</span>;
      <span class="hljs-keyword">case</span> <span class="hljs-string">'test:start'</span>:
        <span class="hljs-title function_">callback</span>(<span class="hljs-literal">null</span>, <span class="hljs-string">`test <span class="hljs-subst">${event.data.name}</span> started`</span>);
        <span class="hljs-keyword">break</span>;
      <span class="hljs-keyword">case</span> <span class="hljs-string">'test:pass'</span>:
        <span class="hljs-title function_">callback</span>(<span class="hljs-literal">null</span>, <span class="hljs-string">`test <span class="hljs-subst">${event.data.name}</span> passed`</span>);
        <span class="hljs-keyword">break</span>;
      <span class="hljs-keyword">case</span> <span class="hljs-string">'test:fail'</span>:
        <span class="hljs-title function_">callback</span>(<span class="hljs-literal">null</span>, <span class="hljs-string">`test <span class="hljs-subst">${event.data.name}</span> failed`</span>);
        <span class="hljs-keyword">break</span>;
      <span class="hljs-keyword">case</span> <span class="hljs-string">'test:plan'</span>:
        <span class="hljs-title function_">callback</span>(<span class="hljs-literal">null</span>, <span class="hljs-string">'test plan'</span>);
        <span class="hljs-keyword">break</span>;
      <span class="hljs-keyword">case</span> <span class="hljs-string">'test:diagnostic'</span>:
      <span class="hljs-keyword">case</span> <span class="hljs-string">'test:stderr'</span>:
      <span class="hljs-keyword">case</span> <span class="hljs-string">'test:stdout'</span>:
        <span class="hljs-title function_">callback</span>(<span class="hljs-literal">null</span>, event.<span class="hljs-property">data</span>.<span class="hljs-property">message</span>);
        <span class="hljs-keyword">break</span>;
      <span class="hljs-keyword">case</span> <span class="hljs-string">'test:coverage'</span>: {
        <span class="hljs-keyword">const</span> { totalLineCount } = event.<span class="hljs-property">data</span>.<span class="hljs-property">summary</span>.<span class="hljs-property">totals</span>;
        <span class="hljs-title function_">callback</span>(<span class="hljs-literal">null</span>, <span class="hljs-string">`total line count: <span class="hljs-subst">${totalLineCount}</span>\n`</span>);
        <span class="hljs-keyword">break</span>;
      }
    }
  },
});

<span class="hljs-variable language_">module</span>.<span class="hljs-property">exports</span> = customReporter;</code><button class="copy-button">copy</button></pre>
<p>Example of a custom reporter using a generator function:</p>

<pre class="with-58-chars"><input class="js-flavor-toggle" type="checkbox" checked aria-label="Show modern ES modules syntax"><code class="language-js mjs"><span class="hljs-keyword">export</span> <span class="hljs-keyword">default</span> <span class="hljs-keyword">async</span> <span class="hljs-keyword">function</span> * <span class="hljs-title function_">customReporter</span>(<span class="hljs-params">source</span>) {
  <span class="hljs-keyword">for</span> <span class="hljs-title function_">await</span> (<span class="hljs-keyword">const</span> event <span class="hljs-keyword">of</span> source) {
    <span class="hljs-keyword">switch</span> (event.<span class="hljs-property">type</span>) {
      <span class="hljs-keyword">case</span> <span class="hljs-string">'test:dequeue'</span>:
        <span class="hljs-keyword">yield</span> <span class="hljs-string">`test <span class="hljs-subst">${event.data.name}</span> dequeued\n`</span>;
        <span class="hljs-keyword">break</span>;
      <span class="hljs-keyword">case</span> <span class="hljs-string">'test:enqueue'</span>:
        <span class="hljs-keyword">yield</span> <span class="hljs-string">`test <span class="hljs-subst">${event.data.name}</span> enqueued\n`</span>;
        <span class="hljs-keyword">break</span>;
      <span class="hljs-keyword">case</span> <span class="hljs-string">'test:watch:drained'</span>:
        <span class="hljs-keyword">yield</span> <span class="hljs-string">'test watch queue drained\n'</span>;
        <span class="hljs-keyword">break</span>;
      <span class="hljs-keyword">case</span> <span class="hljs-string">'test:start'</span>:
        <span class="hljs-keyword">yield</span> <span class="hljs-string">`test <span class="hljs-subst">${event.data.name}</span> started\n`</span>;
        <span class="hljs-keyword">break</span>;
      <span class="hljs-keyword">case</span> <span class="hljs-string">'test:pass'</span>:
        <span class="hljs-keyword">yield</span> <span class="hljs-string">`test <span class="hljs-subst">${event.data.name}</span> passed\n`</span>;
        <span class="hljs-keyword">break</span>;
      <span class="hljs-keyword">case</span> <span class="hljs-string">'test:fail'</span>:
        <span class="hljs-keyword">yield</span> <span class="hljs-string">`test <span class="hljs-subst">${event.data.name}</span> failed\n`</span>;
        <span class="hljs-keyword">break</span>;
      <span class="hljs-keyword">case</span> <span class="hljs-string">'test:plan'</span>:
        <span class="hljs-keyword">yield</span> <span class="hljs-string">'test plan\n'</span>;
        <span class="hljs-keyword">break</span>;
      <span class="hljs-keyword">case</span> <span class="hljs-string">'test:diagnostic'</span>:
      <span class="hljs-keyword">case</span> <span class="hljs-string">'test:stderr'</span>:
      <span class="hljs-keyword">case</span> <span class="hljs-string">'test:stdout'</span>:
        <span class="hljs-keyword">yield</span> <span class="hljs-string">`<span class="hljs-subst">${event.data.message}</span>\n`</span>;
        <span class="hljs-keyword">break</span>;
      <span class="hljs-keyword">case</span> <span class="hljs-string">'test:coverage'</span>: {
        <span class="hljs-keyword">const</span> { totalLineCount } = event.<span class="hljs-property">data</span>.<span class="hljs-property">summary</span>.<span class="hljs-property">totals</span>;
        <span class="hljs-keyword">yield</span> <span class="hljs-string">`total line count: <span class="hljs-subst">${totalLineCount}</span>\n`</span>;
        <span class="hljs-keyword">break</span>;
      }
    }
  }
}</code><code class="language-js cjs"><span class="hljs-variable language_">module</span>.<span class="hljs-property">exports</span> = <span class="hljs-keyword">async</span> <span class="hljs-keyword">function</span> * <span class="hljs-title function_">customReporter</span>(<span class="hljs-params">source</span>) {
  <span class="hljs-keyword">for</span> <span class="hljs-title function_">await</span> (<span class="hljs-keyword">const</span> event <span class="hljs-keyword">of</span> source) {
    <span class="hljs-keyword">switch</span> (event.<span class="hljs-property">type</span>) {
      <span class="hljs-keyword">case</span> <span class="hljs-string">'test:dequeue'</span>:
        <span class="hljs-keyword">yield</span> <span class="hljs-string">`test <span class="hljs-subst">${event.data.name}</span> dequeued\n`</span>;
        <span class="hljs-keyword">break</span>;
      <span class="hljs-keyword">case</span> <span class="hljs-string">'test:enqueue'</span>:
        <span class="hljs-keyword">yield</span> <span class="hljs-string">`test <span class="hljs-subst">${event.data.name}</span> enqueued\n`</span>;
        <span class="hljs-keyword">break</span>;
      <span class="hljs-keyword">case</span> <span class="hljs-string">'test:watch:drained'</span>:
        <span class="hljs-keyword">yield</span> <span class="hljs-string">'test watch queue drained\n'</span>;
        <span class="hljs-keyword">break</span>;
      <span class="hljs-keyword">case</span> <span class="hljs-string">'test:start'</span>:
        <span class="hljs-keyword">yield</span> <span class="hljs-string">`test <span class="hljs-subst">${event.data.name}</span> started\n`</span>;
        <span class="hljs-keyword">break</span>;
      <span class="hljs-keyword">case</span> <span class="hljs-string">'test:pass'</span>:
        <span class="hljs-keyword">yield</span> <span class="hljs-string">`test <span class="hljs-subst">${event.data.name}</span> passed\n`</span>;
        <span class="hljs-keyword">break</span>;
      <span class="hljs-keyword">case</span> <span class="hljs-string">'test:fail'</span>:
        <span class="hljs-keyword">yield</span> <span class="hljs-string">`test <span class="hljs-subst">${event.data.name}</span> failed\n`</span>;
        <span class="hljs-keyword">break</span>;
      <span class="hljs-keyword">case</span> <span class="hljs-string">'test:plan'</span>:
        <span class="hljs-keyword">yield</span> <span class="hljs-string">'test plan\n'</span>;
        <span class="hljs-keyword">break</span>;
      <span class="hljs-keyword">case</span> <span class="hljs-string">'test:diagnostic'</span>:
      <span class="hljs-keyword">case</span> <span class="hljs-string">'test:stderr'</span>:
      <span class="hljs-keyword">case</span> <span class="hljs-string">'test:stdout'</span>:
        <span class="hljs-keyword">yield</span> <span class="hljs-string">`<span class="hljs-subst">${event.data.message}</span>\n`</span>;
        <span class="hljs-keyword">break</span>;
      <span class="hljs-keyword">case</span> <span class="hljs-string">'test:coverage'</span>: {
        <span class="hljs-keyword">const</span> { totalLineCount } = event.<span class="hljs-property">data</span>.<span class="hljs-property">summary</span>.<span class="hljs-property">totals</span>;
        <span class="hljs-keyword">yield</span> <span class="hljs-string">`total line count: <span class="hljs-subst">${totalLineCount}</span>\n`</span>;
        <span class="hljs-keyword">break</span>;
      }
    }
  }
};</code><button class="copy-button">copy</button></pre>
<p>The value provided to <code>--test-reporter</code> should be a string like one used in an
<code>import()</code> in JavaScript code, or a value provided for <a href="cli.html#--importmodule"><code>--import</code></a>.</p>
<h4>Multiple reporters<span><a class="mark" href="#multiple-reporters" id="multiple-reporters">#</a></span><a aria-hidden="true" class="legacy" id="test_multiple_reporters"></a></h4>
<p>The <a href="cli.html#--test-reporter"><code>--test-reporter</code></a> flag can be specified multiple times to report test
results in several formats. In this situation
it is required to specify a destination for each reporter
using <a href="cli.html#--test-reporter-destination"><code>--test-reporter-destination</code></a>.
Destination can be <code>stdout</code>, <code>stderr</code>, or a file path.
Reporters and destinations are paired according
to the order they were specified.</p>
<p>In the following example, the <code>spec</code> reporter will output to <code>stdout</code>,
and the <code>dot</code> reporter will output to <code>file.txt</code>:</p>
<pre><code class="language-bash">node --test-reporter=spec --test-reporter=dot --test-reporter-destination=stdout --test-reporter-destination=file.txt</code> <button class="copy-button">copy</button></pre>
<p>When a single reporter is specified, the destination will default to <code>stdout</code>,
unless a destination is explicitly provided.</p>
</section><section><h3><code>run([options])</code><span><a class="mark" href="#runoptions" id="runoptions">#</a></span><a aria-hidden="true" class="legacy" id="test_run_options"></a></h3>
<div class="api_metadata">
<details class="changelog"><summary>History</summary>
<table>
<tbody><tr><th>Version</th><th>Changes</th></tr>
<tr><td>v22.10.0</td>
<td><p>Added coverage options.</p></td></tr>
<tr><td>v22.8.0</td>
<td><p>Added the <code>isolation</code> option.</p></td></tr>
<tr><td>v22.6.0</td>
<td><p>Added the <code>globPatterns</code> option.</p></td></tr>
<tr><td>v22.0.0</td>
<td><p>Added the <code>forceExit</code> option.</p></td></tr>
<tr><td>v20.1.0, v18.17.0</td>
<td><p>Add a testNamePatterns option.</p></td></tr>
<tr><td>v18.9.0, v16.19.0</td>
<td><p><span>Added in: v18.9.0, v16.19.0</span></p></td></tr>
</tbody></table>
</details>
</div>
<ul>
<li><code>options</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type">&#x3C;Object></a> Configuration options for running tests. The following
properties are supported:
<ul>
<li><code>concurrency</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type">&#x3C;number></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type">&#x3C;boolean></a> If a number is provided,
then that many test processes would run in parallel, where each process
corresponds to one test file.
If <code>true</code>, it would run <code>os.availableParallelism() - 1</code> test files in
parallel.
If <code>false</code>, it would only run one test file at a time.
<strong>Default:</strong> <code>false</code>.</li>
<li><code>files</code>: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array" class="type">&#x3C;Array></a> An array containing the list of files to run.
<strong>Default:</strong> matching files from <a href="#test-runner-execution-model">test runner execution model</a>.</li>
<li><code>forceExit</code>: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type">&#x3C;boolean></a> Configures the test runner to exit the process once
all known tests have finished executing even if the event loop would
otherwise remain active. <strong>Default:</strong> <code>false</code>.</li>
<li><code>globPatterns</code>: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array" class="type">&#x3C;Array></a> An array containing the list of glob patterns to
match test files. This option cannot be used together with <code>files</code>.
<strong>Default:</strong> matching files from <a href="#test-runner-execution-model">test runner execution model</a>.</li>
<li><code>inspectPort</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type">&#x3C;number></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type">&#x3C;Function></a> Sets inspector port of test child process.
This can be a number, or a function that takes no arguments and returns a
number. If a nullish value is provided, each process gets its own port,
incremented from the primary's <code>process.debugPort</code>. This option is ignored
if the <code>isolation</code> option is set to <code>'none'</code> as no child processes are
spawned. <strong>Default:</strong> <code>undefined</code>.</li>
<li><code>isolation</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type">&#x3C;string></a> Configures the type of test isolation. If set to
<code>'process'</code>, each test file is run in a separate child process. If set to
<code>'none'</code>, all test files run in the current process. <strong>Default:</strong>
<code>'process'</code>.</li>
<li><code>only</code>: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type">&#x3C;boolean></a> If truthy, the test context will only run tests that
have the <code>only</code> option set</li>
<li><code>setup</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type">&#x3C;Function></a> A function that accepts the <code>TestsStream</code> instance
and can be used to setup listeners before any tests are run.
<strong>Default:</strong> <code>undefined</code>.</li>
<li><code>execArgv</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array" class="type">&#x3C;Array></a> An array of CLI flags to pass to the <code>node</code> executable when
spawning the subprocesses. This option has no effect when <code>isolation</code> is <code>'none</code>'.
<strong>Default:</strong> <code>[]</code></li>
<li><code>argv</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array" class="type">&#x3C;Array></a> An array of CLI flags to pass to each test file when spawning the
subprocesses. This option has no effect when <code>isolation</code> is <code>'none'</code>.
<strong>Default:</strong> <code>[]</code>.</li>
<li><code>signal</code> <a href="globals.html#class-abortsignal" class="type">&#x3C;AbortSignal></a> Allows aborting an in-progress test execution.</li>
<li><code>testNamePatterns</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type">&#x3C;string></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/RegExp" class="type">&#x3C;RegExp></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array" class="type">&#x3C;Array></a> A String, RegExp or a RegExp Array,
that can be used to only run tests whose name matches the provided pattern.
Test name patterns are interpreted as JavaScript regular expressions.
For each test that is executed, any corresponding test hooks, such as
<code>beforeEach()</code>, are also run.
<strong>Default:</strong> <code>undefined</code>.</li>
<li><code>testSkipPatterns</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type">&#x3C;string></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/RegExp" class="type">&#x3C;RegExp></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array" class="type">&#x3C;Array></a> A String, RegExp or a RegExp Array,
that can be used to exclude running tests whose name matches the provided pattern.
Test name patterns are interpreted as JavaScript regular expressions.
For each test that is executed, any corresponding test hooks, such as
<code>beforeEach()</code>, are also run.
<strong>Default:</strong> <code>undefined</code>.</li>
<li><code>timeout</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type">&#x3C;number></a> A number of milliseconds the test execution will
fail after.
If unspecified, subtests inherit this value from their parent.
<strong>Default:</strong> <code>Infinity</code>.</li>
<li><code>watch</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type">&#x3C;boolean></a> Whether to run in watch mode or not. <strong>Default:</strong> <code>false</code>.</li>
<li><code>shard</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type">&#x3C;Object></a> Running tests in a specific shard. <strong>Default:</strong> <code>undefined</code>.
<ul>
<li><code>index</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type">&#x3C;number></a> is a positive integer between 1 and <code>&#x3C;total></code>
that specifies the index of the shard to run. This option is <em>required</em>.</li>
<li><code>total</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type">&#x3C;number></a> is a positive integer that specifies the total number
of shards to split the test files to. This option is <em>required</em>.</li>
</ul>
</li>
<li><code>coverage</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type">&#x3C;boolean></a> enable <a href="#collecting-code-coverage">code coverage</a> collection.
<strong>Default:</strong> <code>false</code>.</li>
<li><code>coverageExcludeGlobs</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type">&#x3C;string></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array" class="type">&#x3C;Array></a> Excludes specific files from code coverage
using a glob pattern, which can match both absolute and relative file paths.
This property is only applicable when <code>coverage</code> was set to <code>true</code>.
If both <code>coverageExcludeGlobs</code> and <code>coverageIncludeGlobs</code> are provided,
files must meet <strong>both</strong> criteria to be included in the coverage report.
<strong>Default:</strong> <code>undefined</code>.</li>
<li><code>coverageIncludeGlobs</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type">&#x3C;string></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array" class="type">&#x3C;Array></a> Includes specific files in code coverage
using a glob pattern, which can match both absolute and relative file paths.
This property is only applicable when <code>coverage</code> was set to <code>true</code>.
If both <code>coverageExcludeGlobs</code> and <code>coverageIncludeGlobs</code> are provided,
files must meet <strong>both</strong> criteria to be included in the coverage report.
<strong>Default:</strong> <code>undefined</code>.</li>
<li><code>lineCoverage</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type">&#x3C;number></a> Require a minimum percent of covered lines. If code
coverage does not reach the threshold specified, the process will exit with code <code>1</code>.
<strong>Default:</strong> <code>0</code>.</li>
<li><code>branchCoverage</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type">&#x3C;number></a> Require a minimum percent of covered branches. If code
coverage does not reach the threshold specified, the process will exit with code <code>1</code>.
<strong>Default:</strong> <code>0</code>.</li>
<li><code>functionCoverage</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type">&#x3C;number></a> Require a minimum percent of covered functions. If code
coverage does not reach the threshold specified, the process will exit with code <code>1</code>.
<strong>Default:</strong> <code>0</code>.</li>
</ul>
</li>
<li>Returns: <a href="test.html#class-testsstream" class="type">&#x3C;TestsStream></a></li>
</ul>
<p><strong>Note:</strong> <code>shard</code> is used to horizontally parallelize test running across
machines or processes, ideal for large-scale executions across varied
environments. It's incompatible with <code>watch</code> mode, tailored for rapid
code iteration by automatically rerunning tests on file changes.</p>

<pre class="with-47-chars"><input class="js-flavor-toggle" type="checkbox" checked aria-label="Show modern ES modules syntax"><code class="language-js mjs"><span class="hljs-keyword">import</span> { tap } <span class="hljs-keyword">from</span> <span class="hljs-string">'node:test/reporters'</span>;
<span class="hljs-keyword">import</span> { run } <span class="hljs-keyword">from</span> <span class="hljs-string">'node:test'</span>;
<span class="hljs-keyword">import</span> process <span class="hljs-keyword">from</span> <span class="hljs-string">'node:process'</span>;
<span class="hljs-keyword">import</span> path <span class="hljs-keyword">from</span> <span class="hljs-string">'node:path'</span>;

<span class="hljs-title function_">run</span>({ <span class="hljs-attr">files</span>: [path.<span class="hljs-title function_">resolve</span>(<span class="hljs-string">'./tests/test.js'</span>)] })
 .<span class="hljs-title function_">on</span>(<span class="hljs-string">'test:fail'</span>, <span class="hljs-function">() =></span> {
   process.<span class="hljs-property">exitCode</span> = <span class="hljs-number">1</span>;
 })
 .<span class="hljs-title function_">compose</span>(tap)
 .<span class="hljs-title function_">pipe</span>(process.<span class="hljs-property">stdout</span>);</code><code class="language-js cjs"><span class="hljs-keyword">const</span> { tap } = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:test/reporters'</span>);
<span class="hljs-keyword">const</span> { run } = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:test'</span>);
<span class="hljs-keyword">const</span> path = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:path'</span>);

<span class="hljs-title function_">run</span>({ <span class="hljs-attr">files</span>: [path.<span class="hljs-title function_">resolve</span>(<span class="hljs-string">'./tests/test.js'</span>)] })
 .<span class="hljs-title function_">on</span>(<span class="hljs-string">'test:fail'</span>, <span class="hljs-function">() =></span> {
   process.<span class="hljs-property">exitCode</span> = <span class="hljs-number">1</span>;
 })
 .<span class="hljs-title function_">compose</span>(tap)
 .<span class="hljs-title function_">pipe</span>(process.<span class="hljs-property">stdout</span>);</code><button class="copy-button">copy</button></pre>
</section><section><h3><code>suite([name][, options][, fn])</code><span><a class="mark" href="#suitename-options-fn" id="suitename-options-fn">#</a></span><a aria-hidden="true" class="legacy" id="test_suite_name_options_fn"></a></h3>
<div class="api_metadata">
<span>Added in: v22.0.0</span>
</div>
<ul>
<li><code>name</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type">&#x3C;string></a> The name of the suite, which is displayed when reporting test
results. <strong>Default:</strong> The <code>name</code> property of <code>fn</code>, or <code>'&#x3C;anonymous>'</code> if <code>fn</code>
does not have a name.</li>
<li><code>options</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type">&#x3C;Object></a> Optional configuration options for the suite.
This supports the same options as <code>test([name][, options][, fn])</code>.</li>
<li><code>fn</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type">&#x3C;Function></a> | <a href="https://tc39.es/ecma262/#sec-async-function-constructor" class="type">&#x3C;AsyncFunction></a> The suite function declaring nested tests and
suites. The first argument to this function is a <a href="#class-suitecontext"><code>SuiteContext</code></a> object.
<strong>Default:</strong> A no-op function.</li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise" class="type">&#x3C;Promise></a> Immediately fulfilled with <code>undefined</code>.</li>
</ul>
<p>The <code>suite()</code> function is imported from the <code>node:test</code> module.</p>
</section><section><h3><code>suite.skip([name][, options][, fn])</code><span><a class="mark" href="#suiteskipname-options-fn" id="suiteskipname-options-fn">#</a></span><a aria-hidden="true" class="legacy" id="test_suite_skip_name_options_fn"></a></h3>
<div class="api_metadata">
<span>Added in: v22.0.0</span>
</div>
<p>Shorthand for skipping a suite. This is the same as
<a href="#suitename-options-fn"><code>suite([name], { skip: true }[, fn])</code></a>.</p>
</section><section><h3><code>suite.todo([name][, options][, fn])</code><span><a class="mark" href="#suitetodoname-options-fn" id="suitetodoname-options-fn">#</a></span><a aria-hidden="true" class="legacy" id="test_suite_todo_name_options_fn"></a></h3>
<div class="api_metadata">
<span>Added in: v22.0.0</span>
</div>
<p>Shorthand for marking a suite as <code>TODO</code>. This is the same as
<a href="#suitename-options-fn"><code>suite([name], { todo: true }[, fn])</code></a>.</p>
</section><section><h3><code>suite.only([name][, options][, fn])</code><span><a class="mark" href="#suiteonlyname-options-fn" id="suiteonlyname-options-fn">#</a></span><a aria-hidden="true" class="legacy" id="test_suite_only_name_options_fn"></a></h3>
<div class="api_metadata">
<span>Added in: v22.0.0</span>
</div>
<p>Shorthand for marking a suite as <code>only</code>. This is the same as
<a href="#suitename-options-fn"><code>suite([name], { only: true }[, fn])</code></a>.</p>
</section><section><h3><code>test([name][, options][, fn])</code><span><a class="mark" href="#testname-options-fn" id="testname-options-fn">#</a></span><a aria-hidden="true" class="legacy" id="test_test_name_options_fn"></a></h3>
<div class="api_metadata">
<details class="changelog"><summary>History</summary>
<table>
<tbody><tr><th>Version</th><th>Changes</th></tr>
<tr><td>v20.2.0, v18.17.0</td>
<td><p>Added the <code>skip</code>, <code>todo</code>, and <code>only</code> shorthands.</p></td></tr>
<tr><td>v18.8.0, v16.18.0</td>
<td><p>Add a <code>signal</code> option.</p></td></tr>
<tr><td>v18.7.0, v16.17.0</td>
<td><p>Add a <code>timeout</code> option.</p></td></tr>
<tr><td>v18.0.0, v16.17.0</td>
<td><p><span>Added in: v18.0.0, v16.17.0</span></p></td></tr>
</tbody></table>
</details>
</div>
<ul>
<li><code>name</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type">&#x3C;string></a> The name of the test, which is displayed when reporting test
results. <strong>Default:</strong> The <code>name</code> property of <code>fn</code>, or <code>'&#x3C;anonymous>'</code> if <code>fn</code>
does not have a name.</li>
<li><code>options</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type">&#x3C;Object></a> Configuration options for the test. The following
properties are supported:
<ul>
<li><code>concurrency</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type">&#x3C;number></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type">&#x3C;boolean></a> If a number is provided,
then that many tests would run in parallel within the application thread.
If <code>true</code>, all scheduled asynchronous tests run concurrently within the
thread. If <code>false</code>, only one test runs at a time.
If unspecified, subtests inherit this value from their parent.
<strong>Default:</strong> <code>false</code>.</li>
<li><code>only</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type">&#x3C;boolean></a> If truthy, and the test context is configured to run
<code>only</code> tests, then this test will be run. Otherwise, the test is skipped.
<strong>Default:</strong> <code>false</code>.</li>
<li><code>signal</code> <a href="globals.html#class-abortsignal" class="type">&#x3C;AbortSignal></a> Allows aborting an in-progress test.</li>
<li><code>skip</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type">&#x3C;boolean></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type">&#x3C;string></a> If truthy, the test is skipped. If a string is
provided, that string is displayed in the test results as the reason for
skipping the test. <strong>Default:</strong> <code>false</code>.</li>
<li><code>todo</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type">&#x3C;boolean></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type">&#x3C;string></a> If truthy, the test marked as <code>TODO</code>. If a string
is provided, that string is displayed in the test results as the reason why
the test is <code>TODO</code>. <strong>Default:</strong> <code>false</code>.</li>
<li><code>timeout</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type">&#x3C;number></a> A number of milliseconds the test will fail after.
If unspecified, subtests inherit this value from their parent.
<strong>Default:</strong> <code>Infinity</code>.</li>
<li><code>plan</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type">&#x3C;number></a> The number of assertions and subtests expected to be run in the test.
If the number of assertions run in the test does not match the number
specified in the plan, the test will fail.
<strong>Default:</strong> <code>undefined</code>.</li>
</ul>
</li>
<li><code>fn</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type">&#x3C;Function></a> | <a href="https://tc39.es/ecma262/#sec-async-function-constructor" class="type">&#x3C;AsyncFunction></a> The function under test. The first argument
to this function is a <a href="#class-testcontext"><code>TestContext</code></a> object. If the test uses callbacks,
the callback function is passed as the second argument. <strong>Default:</strong> A no-op
function.</li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise" class="type">&#x3C;Promise></a> Fulfilled with <code>undefined</code> once
the test completes, or immediately if the test runs within a suite.</li>
</ul>
<p>The <code>test()</code> function is the value imported from the <code>test</code> module. Each
invocation of this function results in reporting the test to the <a href="test.html#class-testsstream" class="type">&#x3C;TestsStream></a>.</p>
<p>The <code>TestContext</code> object passed to the <code>fn</code> argument can be used to perform
actions related to the current test. Examples include skipping the test, adding
additional diagnostic information, or creating subtests.</p>
<p><code>test()</code> returns a <code>Promise</code> that fulfills once the test completes.
if <code>test()</code> is called within a suite, it fulfills immediately.
The return value can usually be discarded for top level tests.
However, the return value from subtests should be used to prevent the parent
test from finishing first and cancelling the subtest
as shown in the following example.</p>
<pre><code class="language-js"><span class="hljs-title function_">test</span>(<span class="hljs-string">'top level test'</span>, <span class="hljs-title function_">async</span> (t) => {
  <span class="hljs-comment">// The setTimeout() in the following subtest would cause it to outlive its</span>
  <span class="hljs-comment">// parent test if 'await' is removed on the next line. Once the parent test</span>
  <span class="hljs-comment">// completes, it will cancel any outstanding subtests.</span>
  <span class="hljs-keyword">await</span> t.<span class="hljs-title function_">test</span>(<span class="hljs-string">'longer running subtest'</span>, <span class="hljs-title function_">async</span> (t) => {
    <span class="hljs-keyword">return</span> <span class="hljs-keyword">new</span> <span class="hljs-title class_">Promise</span>(<span class="hljs-function">(<span class="hljs-params">resolve, reject</span>) =></span> {
      <span class="hljs-built_in">setTimeout</span>(resolve, <span class="hljs-number">1000</span>);
    });
  });
});</code> <button class="copy-button">copy</button></pre>
<p>The <code>timeout</code> option can be used to fail the test if it takes longer than
<code>timeout</code> milliseconds to complete. However, it is not a reliable mechanism for
canceling tests because a running test might block the application thread and
thus prevent the scheduled cancellation.</p>
</section><section><h3><code>test.skip([name][, options][, fn])</code><span><a class="mark" href="#testskipname-options-fn" id="testskipname-options-fn">#</a></span><a aria-hidden="true" class="legacy" id="test_test_skip_name_options_fn"></a></h3>
<p>Shorthand for skipping a test,
same as <a href="#testname-options-fn"><code>test([name], { skip: true }[, fn])</code></a>.</p>
</section><section><h3><code>test.todo([name][, options][, fn])</code><span><a class="mark" href="#testtodoname-options-fn" id="testtodoname-options-fn">#</a></span><a aria-hidden="true" class="legacy" id="test_test_todo_name_options_fn"></a></h3>
<p>Shorthand for marking a test as <code>TODO</code>,
same as <a href="#testname-options-fn"><code>test([name], { todo: true }[, fn])</code></a>.</p>
</section><section><h3><code>test.only([name][, options][, fn])</code><span><a class="mark" href="#testonlyname-options-fn" id="testonlyname-options-fn">#</a></span><a aria-hidden="true" class="legacy" id="test_test_only_name_options_fn"></a></h3>
<p>Shorthand for marking a test as <code>only</code>,
same as <a href="#testname-options-fn"><code>test([name], { only: true }[, fn])</code></a>.</p>
</section><section><h3><code>describe([name][, options][, fn])</code><span><a class="mark" href="#describename-options-fn" id="describename-options-fn">#</a></span><a aria-hidden="true" class="legacy" id="test_describe_name_options_fn"></a></h3>
<p>Alias for <a href="#suitename-options-fn"><code>suite()</code></a>.</p>
<p>The <code>describe()</code> function is imported from the <code>node:test</code> module.</p>
</section><section><h3><code>describe.skip([name][, options][, fn])</code><span><a class="mark" href="#describeskipname-options-fn" id="describeskipname-options-fn">#</a></span><a aria-hidden="true" class="legacy" id="test_describe_skip_name_options_fn"></a></h3>
<p>Shorthand for skipping a suite. This is the same as
<a href="#describename-options-fn"><code>describe([name], { skip: true }[, fn])</code></a>.</p>
</section><section><h3><code>describe.todo([name][, options][, fn])</code><span><a class="mark" href="#describetodoname-options-fn" id="describetodoname-options-fn">#</a></span><a aria-hidden="true" class="legacy" id="test_describe_todo_name_options_fn"></a></h3>
<p>Shorthand for marking a suite as <code>TODO</code>. This is the same as
<a href="#describename-options-fn"><code>describe([name], { todo: true }[, fn])</code></a>.</p>
</section><section><h3><code>describe.only([name][, options][, fn])</code><span><a class="mark" href="#describeonlyname-options-fn" id="describeonlyname-options-fn">#</a></span><a aria-hidden="true" class="legacy" id="test_describe_only_name_options_fn"></a></h3>
<div class="api_metadata">
<span>Added in: v19.8.0, v18.15.0</span>
</div>
<p>Shorthand for marking a suite as <code>only</code>. This is the same as
<a href="#describename-options-fn"><code>describe([name], { only: true }[, fn])</code></a>.</p>
</section><section><h3><code>it([name][, options][, fn])</code><span><a class="mark" href="#itname-options-fn" id="itname-options-fn">#</a></span><a aria-hidden="true" class="legacy" id="test_it_name_options_fn"></a></h3>
<div class="api_metadata">
<details class="changelog"><summary>History</summary>
<table>
<tbody><tr><th>Version</th><th>Changes</th></tr>
<tr><td>v19.8.0, v18.16.0</td>
<td><p>Calling <code>it()</code> is now equivalent to calling <code>test()</code>.</p></td></tr>
<tr><td>v18.6.0, v16.17.0</td>
<td><p><span>Added in: v18.6.0, v16.17.0</span></p></td></tr>
</tbody></table>
</details>
</div>
<p>Alias for <a href="#testname-options-fn"><code>test()</code></a>.</p>
<p>The <code>it()</code> function is imported from the <code>node:test</code> module.</p>
</section><section><h3><code>it.skip([name][, options][, fn])</code><span><a class="mark" href="#itskipname-options-fn" id="itskipname-options-fn">#</a></span><a aria-hidden="true" class="legacy" id="test_it_skip_name_options_fn"></a></h3>
<p>Shorthand for skipping a test,
same as <a href="#testname-options-fn"><code>it([name], { skip: true }[, fn])</code></a>.</p>
</section><section><h3><code>it.todo([name][, options][, fn])</code><span><a class="mark" href="#ittodoname-options-fn" id="ittodoname-options-fn">#</a></span><a aria-hidden="true" class="legacy" id="test_it_todo_name_options_fn"></a></h3>
<p>Shorthand for marking a test as <code>TODO</code>,
same as <a href="#testname-options-fn"><code>it([name], { todo: true }[, fn])</code></a>.</p>
</section><section><h3><code>it.only([name][, options][, fn])</code><span><a class="mark" href="#itonlyname-options-fn" id="itonlyname-options-fn">#</a></span><a aria-hidden="true" class="legacy" id="test_it_only_name_options_fn"></a></h3>
<div class="api_metadata">
<span>Added in: v19.8.0, v18.15.0</span>
</div>
<p>Shorthand for marking a test as <code>only</code>,
same as <a href="#testname-options-fn"><code>it([name], { only: true }[, fn])</code></a>.</p>
</section><section><h3><code>before([fn][, options])</code><span><a class="mark" href="#beforefn-options" id="beforefn-options">#</a></span><a aria-hidden="true" class="legacy" id="test_before_fn_options"></a></h3>
<div class="api_metadata">
<span>Added in: v18.8.0, v16.18.0</span>
</div>
<ul>
<li><code>fn</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type">&#x3C;Function></a> | <a href="https://tc39.es/ecma262/#sec-async-function-constructor" class="type">&#x3C;AsyncFunction></a> The hook function.
If the hook uses callbacks,
the callback function is passed as the second argument. <strong>Default:</strong> A no-op
function.</li>
<li><code>options</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type">&#x3C;Object></a> Configuration options for the hook. The following
properties are supported:
<ul>
<li><code>signal</code> <a href="globals.html#class-abortsignal" class="type">&#x3C;AbortSignal></a> Allows aborting an in-progress hook.</li>
<li><code>timeout</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type">&#x3C;number></a> A number of milliseconds the hook will fail after.
If unspecified, subtests inherit this value from their parent.
<strong>Default:</strong> <code>Infinity</code>.</li>
</ul>
</li>
</ul>
<p>This function creates a hook that runs before executing a suite.</p>
<pre><code class="language-js"><span class="hljs-title function_">describe</span>(<span class="hljs-string">'tests'</span>, <span class="hljs-title function_">async</span> () => {
  <span class="hljs-title function_">before</span>(<span class="hljs-function">() =></span> <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(<span class="hljs-string">'about to run some test'</span>));
  <span class="hljs-title function_">it</span>(<span class="hljs-string">'is a subtest'</span>, <span class="hljs-function">() =></span> {
    assert.<span class="hljs-title function_">ok</span>(<span class="hljs-string">'some relevant assertion here'</span>);
  });
});</code> <button class="copy-button">copy</button></pre>
</section><section><h3><code>after([fn][, options])</code><span><a class="mark" href="#afterfn-options" id="afterfn-options">#</a></span><a aria-hidden="true" class="legacy" id="test_after_fn_options"></a></h3>
<div class="api_metadata">
<span>Added in: v18.8.0, v16.18.0</span>
</div>
<ul>
<li><code>fn</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type">&#x3C;Function></a> | <a href="https://tc39.es/ecma262/#sec-async-function-constructor" class="type">&#x3C;AsyncFunction></a> The hook function.
If the hook uses callbacks,
the callback function is passed as the second argument. <strong>Default:</strong> A no-op
function.</li>
<li><code>options</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type">&#x3C;Object></a> Configuration options for the hook. The following
properties are supported:
<ul>
<li><code>signal</code> <a href="globals.html#class-abortsignal" class="type">&#x3C;AbortSignal></a> Allows aborting an in-progress hook.</li>
<li><code>timeout</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type">&#x3C;number></a> A number of milliseconds the hook will fail after.
If unspecified, subtests inherit this value from their parent.
<strong>Default:</strong> <code>Infinity</code>.</li>
</ul>
</li>
</ul>
<p>This function creates a hook that runs after executing a suite.</p>
<pre><code class="language-js"><span class="hljs-title function_">describe</span>(<span class="hljs-string">'tests'</span>, <span class="hljs-title function_">async</span> () => {
  <span class="hljs-title function_">after</span>(<span class="hljs-function">() =></span> <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(<span class="hljs-string">'finished running tests'</span>));
  <span class="hljs-title function_">it</span>(<span class="hljs-string">'is a subtest'</span>, <span class="hljs-function">() =></span> {
    assert.<span class="hljs-title function_">ok</span>(<span class="hljs-string">'some relevant assertion here'</span>);
  });
});</code> <button class="copy-button">copy</button></pre>
<p><strong>Note:</strong> The <code>after</code> hook is guaranteed to run,
even if tests within the suite fail.</p>
</section><section><h3><code>beforeEach([fn][, options])</code><span><a class="mark" href="#beforeeachfn-options" id="beforeeachfn-options">#</a></span><a aria-hidden="true" class="legacy" id="test_beforeeach_fn_options"></a></h3>
<div class="api_metadata">
<span>Added in: v18.8.0, v16.18.0</span>
</div>
<ul>
<li><code>fn</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type">&#x3C;Function></a> | <a href="https://tc39.es/ecma262/#sec-async-function-constructor" class="type">&#x3C;AsyncFunction></a> The hook function.
If the hook uses callbacks,
the callback function is passed as the second argument. <strong>Default:</strong> A no-op
function.</li>
<li><code>options</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type">&#x3C;Object></a> Configuration options for the hook. The following
properties are supported:
<ul>
<li><code>signal</code> <a href="globals.html#class-abortsignal" class="type">&#x3C;AbortSignal></a> Allows aborting an in-progress hook.</li>
<li><code>timeout</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type">&#x3C;number></a> A number of milliseconds the hook will fail after.
If unspecified, subtests inherit this value from their parent.
<strong>Default:</strong> <code>Infinity</code>.</li>
</ul>
</li>
</ul>
<p>This function creates a hook that runs before each test in the current suite.</p>
<pre><code class="language-js"><span class="hljs-title function_">describe</span>(<span class="hljs-string">'tests'</span>, <span class="hljs-title function_">async</span> () => {
  <span class="hljs-title function_">beforeEach</span>(<span class="hljs-function">() =></span> <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(<span class="hljs-string">'about to run a test'</span>));
  <span class="hljs-title function_">it</span>(<span class="hljs-string">'is a subtest'</span>, <span class="hljs-function">() =></span> {
    assert.<span class="hljs-title function_">ok</span>(<span class="hljs-string">'some relevant assertion here'</span>);
  });
});</code> <button class="copy-button">copy</button></pre>
</section><section><h3><code>afterEach([fn][, options])</code><span><a class="mark" href="#aftereachfn-options" id="aftereachfn-options">#</a></span><a aria-hidden="true" class="legacy" id="test_aftereach_fn_options"></a></h3>
<div class="api_metadata">
<span>Added in: v18.8.0, v16.18.0</span>
</div>
<ul>
<li><code>fn</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type">&#x3C;Function></a> | <a href="https://tc39.es/ecma262/#sec-async-function-constructor" class="type">&#x3C;AsyncFunction></a> The hook function.
If the hook uses callbacks,
the callback function is passed as the second argument. <strong>Default:</strong> A no-op
function.</li>
<li><code>options</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type">&#x3C;Object></a> Configuration options for the hook. The following
properties are supported:
<ul>
<li><code>signal</code> <a href="globals.html#class-abortsignal" class="type">&#x3C;AbortSignal></a> Allows aborting an in-progress hook.</li>
<li><code>timeout</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type">&#x3C;number></a> A number of milliseconds the hook will fail after.
If unspecified, subtests inherit this value from their parent.
<strong>Default:</strong> <code>Infinity</code>.</li>
</ul>
</li>
</ul>
<p>This function creates a hook that runs after each test in the current suite.
The <code>afterEach()</code> hook is run even if the test fails.</p>
<pre><code class="language-js"><span class="hljs-title function_">describe</span>(<span class="hljs-string">'tests'</span>, <span class="hljs-title function_">async</span> () => {
  <span class="hljs-title function_">afterEach</span>(<span class="hljs-function">() =></span> <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(<span class="hljs-string">'finished running a test'</span>));
  <span class="hljs-title function_">it</span>(<span class="hljs-string">'is a subtest'</span>, <span class="hljs-function">() =></span> {
    assert.<span class="hljs-title function_">ok</span>(<span class="hljs-string">'some relevant assertion here'</span>);
  });
});</code> <button class="copy-button">copy</button></pre>
</section><section><h3><code>assert</code><span><a class="mark" href="#assert" id="assert">#</a></span><a aria-hidden="true" class="legacy" id="test_assert"></a></h3>
<div class="api_metadata">
<span>Added in: v22.14.0</span>
</div>
<p>An object whose methods are used to configure available assertions on the
<code>TestContext</code> objects in the current process. The methods from <code>node:assert</code>
and snapshot testing functions are available by default.</p>
<p>It is possible to apply the same configuration to all files by placing common
configuration code in a module
preloaded with <code>--require</code> or <code>--import</code>.</p>
<h4><code>assert.register(name, fn)</code><span><a class="mark" href="#assertregistername-fn" id="assertregistername-fn">#</a></span><a aria-hidden="true" class="legacy" id="test_assert_register_name_fn"></a></h4>
<div class="api_metadata">
<span>Added in: v22.14.0</span>
</div>
<p>Defines a new assertion function with the provided name and function. If an
assertion already exists with the same name, it is overwritten.</p>
</section><section><h3><code>snapshot</code><span><a class="mark" href="#snapshot" id="snapshot">#</a></span><a aria-hidden="true" class="legacy" id="test_snapshot"></a></h3>
<div class="api_metadata">
<span>Added in: v22.3.0</span>
</div>
<p>An object whose methods are used to configure default snapshot settings in the
current process. It is possible to apply the same configuration to all files by
placing common configuration code in a module preloaded with <code>--require</code> or
<code>--import</code>.</p>
<h4><code>snapshot.setDefaultSnapshotSerializers(serializers)</code><span><a class="mark" href="#snapshotsetdefaultsnapshotserializersserializers" id="snapshotsetdefaultsnapshotserializersserializers">#</a></span><a aria-hidden="true" class="legacy" id="test_snapshot_setdefaultsnapshotserializers_serializers"></a></h4>
<div class="api_metadata">
<span>Added in: v22.3.0</span>
</div>
<ul>
<li><code>serializers</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array" class="type">&#x3C;Array></a> An array of synchronous functions used as the default
serializers for snapshot tests.</li>
</ul>
<p>This function is used to customize the default serialization mechanism used by
the test runner. By default, the test runner performs serialization by calling
<code>JSON.stringify(value, null, 2)</code> on the provided value. <code>JSON.stringify()</code> does
have limitations regarding circular structures and supported data types. If a
more robust serialization mechanism is required, this function should be used.</p>
<h4><code>snapshot.setResolveSnapshotPath(fn)</code><span><a class="mark" href="#snapshotsetresolvesnapshotpathfn" id="snapshotsetresolvesnapshotpathfn">#</a></span><a aria-hidden="true" class="legacy" id="test_snapshot_setresolvesnapshotpath_fn"></a></h4>
<div class="api_metadata">
<span>Added in: v22.3.0</span>
</div>
<ul>
<li><code>fn</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type">&#x3C;Function></a> A function used to compute the location of the snapshot file.
The function receives the path of the test file as its only argument. If the
test is not associated with a file (for example in the REPL), the input is
undefined. <code>fn()</code> must return a string specifying the location of the snapshot
snapshot file.</li>
</ul>
<p>This function is used to customize the location of the snapshot file used for
snapshot testing. By default, the snapshot filename is the same as the entry
point filename with a <code>.snapshot</code> file extension.</p>
</section><section><h3>Class: <code>MockFunctionContext</code><span><a class="mark" href="#class-mockfunctioncontext" id="class-mockfunctioncontext">#</a></span><a aria-hidden="true" class="legacy" id="test_class_mockfunctioncontext"></a></h3>
<div class="api_metadata">
<span>Added in: v19.1.0, v18.13.0</span>
</div>
<p>The <code>MockFunctionContext</code> class is used to inspect or manipulate the behavior of
mocks created via the <a href="#class-mocktracker"><code>MockTracker</code></a> APIs.</p>
<h4><code>ctx.calls</code><span><a class="mark" href="#ctxcalls" id="ctxcalls">#</a></span><a aria-hidden="true" class="legacy" id="test_ctx_calls"></a></h4>
<div class="api_metadata">
<span>Added in: v19.1.0, v18.13.0</span>
</div>
<ul>
<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array" class="type">&#x3C;Array></a></li>
</ul>
<p>A getter that returns a copy of the internal array used to track calls to the
mock. Each entry in the array is an object with the following properties.</p>
<ul>
<li><code>arguments</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array" class="type">&#x3C;Array></a> An array of the arguments passed to the mock function.</li>
<li><code>error</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type">&#x3C;any></a> If the mocked function threw then this property contains the
thrown value. <strong>Default:</strong> <code>undefined</code>.</li>
<li><code>result</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type">&#x3C;any></a> The value returned by the mocked function.</li>
<li><code>stack</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error" class="type">&#x3C;Error></a> An <code>Error</code> object whose stack can be used to determine the
callsite of the mocked function invocation.</li>
<li><code>target</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type">&#x3C;Function></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Undefined_type" class="type">&#x3C;undefined></a> If the mocked function is a constructor, this
field contains the class being constructed. Otherwise this will be
<code>undefined</code>.</li>
<li><code>this</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type">&#x3C;any></a> The mocked function's <code>this</code> value.</li>
</ul>
<h4><code>ctx.callCount()</code><span><a class="mark" href="#ctxcallcount" id="ctxcallcount">#</a></span><a aria-hidden="true" class="legacy" id="test_ctx_callcount"></a></h4>
<div class="api_metadata">
<span>Added in: v19.1.0, v18.13.0</span>
</div>
<ul>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type">&#x3C;integer></a> The number of times that this mock has been invoked.</li>
</ul>
<p>This function returns the number of times that this mock has been invoked. This
function is more efficient than checking <code>ctx.calls.length</code> because <code>ctx.calls</code>
is a getter that creates a copy of the internal call tracking array.</p>
<h4><code>ctx.mockImplementation(implementation)</code><span><a class="mark" href="#ctxmockimplementationimplementation" id="ctxmockimplementationimplementation">#</a></span><a aria-hidden="true" class="legacy" id="test_ctx_mockimplementation_implementation"></a></h4>
<div class="api_metadata">
<span>Added in: v19.1.0, v18.13.0</span>
</div>
<ul>
<li><code>implementation</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type">&#x3C;Function></a> | <a href="https://tc39.es/ecma262/#sec-async-function-constructor" class="type">&#x3C;AsyncFunction></a> The function to be used as the
mock's new implementation.</li>
</ul>
<p>This function is used to change the behavior of an existing mock.</p>
<p>The following example creates a mock function using <code>t.mock.fn()</code>, calls the
mock function, and then changes the mock implementation to a different function.</p>
<pre><code class="language-js"><span class="hljs-title function_">test</span>(<span class="hljs-string">'changes a mock behavior'</span>, <span class="hljs-function">(<span class="hljs-params">t</span>) =></span> {
  <span class="hljs-keyword">let</span> cnt = <span class="hljs-number">0</span>;

  <span class="hljs-keyword">function</span> <span class="hljs-title function_">addOne</span>(<span class="hljs-params"></span>) {
    cnt++;
    <span class="hljs-keyword">return</span> cnt;
  }

  <span class="hljs-keyword">function</span> <span class="hljs-title function_">addTwo</span>(<span class="hljs-params"></span>) {
    cnt += <span class="hljs-number">2</span>;
    <span class="hljs-keyword">return</span> cnt;
  }

  <span class="hljs-keyword">const</span> fn = t.<span class="hljs-property">mock</span>.<span class="hljs-title function_">fn</span>(addOne);

  assert.<span class="hljs-title function_">strictEqual</span>(<span class="hljs-title function_">fn</span>(), <span class="hljs-number">1</span>);
  fn.<span class="hljs-property">mock</span>.<span class="hljs-title function_">mockImplementation</span>(addTwo);
  assert.<span class="hljs-title function_">strictEqual</span>(<span class="hljs-title function_">fn</span>(), <span class="hljs-number">3</span>);
  assert.<span class="hljs-title function_">strictEqual</span>(<span class="hljs-title function_">fn</span>(), <span class="hljs-number">5</span>);
});</code> <button class="copy-button">copy</button></pre>
<h4><code>ctx.mockImplementationOnce(implementation[, onCall])</code><span><a class="mark" href="#ctxmockimplementationonceimplementation-oncall" id="ctxmockimplementationonceimplementation-oncall">#</a></span><a aria-hidden="true" class="legacy" id="test_ctx_mockimplementationonce_implementation_oncall"></a></h4>
<div class="api_metadata">
<span>Added in: v19.1.0, v18.13.0</span>
</div>
<ul>
<li><code>implementation</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type">&#x3C;Function></a> | <a href="https://tc39.es/ecma262/#sec-async-function-constructor" class="type">&#x3C;AsyncFunction></a> The function to be used as the
mock's implementation for the invocation number specified by <code>onCall</code>.</li>
<li><code>onCall</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type">&#x3C;integer></a> The invocation number that will use <code>implementation</code>. If
the specified invocation has already occurred then an exception is thrown.
<strong>Default:</strong> The number of the next invocation.</li>
</ul>
<p>This function is used to change the behavior of an existing mock for a single
invocation. Once invocation <code>onCall</code> has occurred, the mock will revert to
whatever behavior it would have used had <code>mockImplementationOnce()</code> not been
called.</p>
<p>The following example creates a mock function using <code>t.mock.fn()</code>, calls the
mock function, changes the mock implementation to a different function for the
next invocation, and then resumes its previous behavior.</p>
<pre><code class="language-js"><span class="hljs-title function_">test</span>(<span class="hljs-string">'changes a mock behavior once'</span>, <span class="hljs-function">(<span class="hljs-params">t</span>) =></span> {
  <span class="hljs-keyword">let</span> cnt = <span class="hljs-number">0</span>;

  <span class="hljs-keyword">function</span> <span class="hljs-title function_">addOne</span>(<span class="hljs-params"></span>) {
    cnt++;
    <span class="hljs-keyword">return</span> cnt;
  }

  <span class="hljs-keyword">function</span> <span class="hljs-title function_">addTwo</span>(<span class="hljs-params"></span>) {
    cnt += <span class="hljs-number">2</span>;
    <span class="hljs-keyword">return</span> cnt;
  }

  <span class="hljs-keyword">const</span> fn = t.<span class="hljs-property">mock</span>.<span class="hljs-title function_">fn</span>(addOne);

  assert.<span class="hljs-title function_">strictEqual</span>(<span class="hljs-title function_">fn</span>(), <span class="hljs-number">1</span>);
  fn.<span class="hljs-property">mock</span>.<span class="hljs-title function_">mockImplementationOnce</span>(addTwo);
  assert.<span class="hljs-title function_">strictEqual</span>(<span class="hljs-title function_">fn</span>(), <span class="hljs-number">3</span>);
  assert.<span class="hljs-title function_">strictEqual</span>(<span class="hljs-title function_">fn</span>(), <span class="hljs-number">4</span>);
});</code> <button class="copy-button">copy</button></pre>
<h4><code>ctx.resetCalls()</code><span><a class="mark" href="#ctxresetcalls" id="ctxresetcalls">#</a></span><a aria-hidden="true" class="legacy" id="test_ctx_resetcalls"></a></h4>
<div class="api_metadata">
<span>Added in: v19.3.0, v18.13.0</span>
</div>
<p>Resets the call history of the mock function.</p>
<h4><code>ctx.restore()</code><span><a class="mark" href="#ctxrestore" id="ctxrestore">#</a></span><a aria-hidden="true" class="legacy" id="test_ctx_restore"></a></h4>
<div class="api_metadata">
<span>Added in: v19.1.0, v18.13.0</span>
</div>
<p>Resets the implementation of the mock function to its original behavior. The
mock can still be used after calling this function.</p>
</section><section><h3>Class: <code>MockModuleContext</code><span><a class="mark" href="#class-mockmodulecontext" id="class-mockmodulecontext">#</a></span><a aria-hidden="true" class="legacy" id="test_class_mockmodulecontext"></a></h3>
<div class="api_metadata">
<span>Added in: v22.3.0</span>
</div>
<p></p><div class="api_stability api_stability_1"><a href="documentation.html#stability-index">Stability: 1</a>.0 - Early development</div><p></p>
<p>The <code>MockModuleContext</code> class is used to manipulate the behavior of module mocks
created via the <a href="#class-mocktracker"><code>MockTracker</code></a> APIs.</p>
<h4><code>ctx.restore()</code><span><a class="mark" href="#ctxrestore_1" id="ctxrestore_1">#</a></span><a aria-hidden="true" class="legacy" id="test_ctx_restore_1"></a></h4>
<div class="api_metadata">
<span>Added in: v22.3.0</span>
</div>
<p>Resets the implementation of the mock module.</p>
</section><section><h3>Class: <code>MockTracker</code><span><a class="mark" href="#class-mocktracker" id="class-mocktracker">#</a></span><a aria-hidden="true" class="legacy" id="test_class_mocktracker"></a></h3>
<div class="api_metadata">
<span>Added in: v19.1.0, v18.13.0</span>
</div>
<p>The <code>MockTracker</code> class is used to manage mocking functionality. The test runner
module provides a top level <code>mock</code> export which is a <code>MockTracker</code> instance.
Each test also provides its own <code>MockTracker</code> instance via the test context's
<code>mock</code> property.</p>
<h4><code>mock.fn([original[, implementation]][, options])</code><span><a class="mark" href="#mockfnoriginal-implementation-options" id="mockfnoriginal-implementation-options">#</a></span><a aria-hidden="true" class="legacy" id="test_mock_fn_original_implementation_options"></a></h4>
<div class="api_metadata">
<span>Added in: v19.1.0, v18.13.0</span>
</div>
<ul>
<li><code>original</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type">&#x3C;Function></a> | <a href="https://tc39.es/ecma262/#sec-async-function-constructor" class="type">&#x3C;AsyncFunction></a> An optional function to create a mock on.
<strong>Default:</strong> A no-op function.</li>
<li><code>implementation</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type">&#x3C;Function></a> | <a href="https://tc39.es/ecma262/#sec-async-function-constructor" class="type">&#x3C;AsyncFunction></a> An optional function used as the
mock implementation for <code>original</code>. This is useful for creating mocks that
exhibit one behavior for a specified number of calls and then restore the
behavior of <code>original</code>. <strong>Default:</strong> The function specified by <code>original</code>.</li>
<li><code>options</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type">&#x3C;Object></a> Optional configuration options for the mock function. The
following properties are supported:
<ul>
<li><code>times</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type">&#x3C;integer></a> The number of times that the mock will use the behavior of
<code>implementation</code>. Once the mock function has been called <code>times</code> times, it
will automatically restore the behavior of <code>original</code>. This value must be an
integer greater than zero. <strong>Default:</strong> <code>Infinity</code>.</li>
</ul>
</li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Proxy" class="type">&#x3C;Proxy></a> The mocked function. The mocked function contains a special
<code>mock</code> property, which is an instance of <a href="#class-mockfunctioncontext"><code>MockFunctionContext</code></a>, and can
be used for inspecting and changing the behavior of the mocked function.</li>
</ul>
<p>This function is used to create a mock function.</p>
<p>The following example creates a mock function that increments a counter by one
on each invocation. The <code>times</code> option is used to modify the mock behavior such
that the first two invocations add two to the counter instead of one.</p>
<pre><code class="language-js"><span class="hljs-title function_">test</span>(<span class="hljs-string">'mocks a counting function'</span>, <span class="hljs-function">(<span class="hljs-params">t</span>) =></span> {
  <span class="hljs-keyword">let</span> cnt = <span class="hljs-number">0</span>;

  <span class="hljs-keyword">function</span> <span class="hljs-title function_">addOne</span>(<span class="hljs-params"></span>) {
    cnt++;
    <span class="hljs-keyword">return</span> cnt;
  }

  <span class="hljs-keyword">function</span> <span class="hljs-title function_">addTwo</span>(<span class="hljs-params"></span>) {
    cnt += <span class="hljs-number">2</span>;
    <span class="hljs-keyword">return</span> cnt;
  }

  <span class="hljs-keyword">const</span> fn = t.<span class="hljs-property">mock</span>.<span class="hljs-title function_">fn</span>(addOne, addTwo, { <span class="hljs-attr">times</span>: <span class="hljs-number">2</span> });

  assert.<span class="hljs-title function_">strictEqual</span>(<span class="hljs-title function_">fn</span>(), <span class="hljs-number">2</span>);
  assert.<span class="hljs-title function_">strictEqual</span>(<span class="hljs-title function_">fn</span>(), <span class="hljs-number">4</span>);
  assert.<span class="hljs-title function_">strictEqual</span>(<span class="hljs-title function_">fn</span>(), <span class="hljs-number">5</span>);
  assert.<span class="hljs-title function_">strictEqual</span>(<span class="hljs-title function_">fn</span>(), <span class="hljs-number">6</span>);
});</code> <button class="copy-button">copy</button></pre>
<h4><code>mock.getter(object, methodName[, implementation][, options])</code><span><a class="mark" href="#mockgetterobject-methodname-implementation-options" id="mockgetterobject-methodname-implementation-options">#</a></span><a aria-hidden="true" class="legacy" id="test_mock_getter_object_methodname_implementation_options"></a></h4>
<div class="api_metadata">
<span>Added in: v19.3.0, v18.13.0</span>
</div>
<p>This function is syntax sugar for <a href="#mockmethodobject-methodname-implementation-options"><code>MockTracker.method</code></a> with <code>options.getter</code>
set to <code>true</code>.</p>
<h4><code>mock.method(object, methodName[, implementation][, options])</code><span><a class="mark" href="#mockmethodobject-methodname-implementation-options" id="mockmethodobject-methodname-implementation-options">#</a></span><a aria-hidden="true" class="legacy" id="test_mock_method_object_methodname_implementation_options"></a></h4>
<div class="api_metadata">
<span>Added in: v19.1.0, v18.13.0</span>
</div>
<ul>
<li><code>object</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type">&#x3C;Object></a> The object whose method is being mocked.</li>
<li><code>methodName</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type">&#x3C;string></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Symbol_type" class="type">&#x3C;symbol></a> The identifier of the method on <code>object</code> to mock.
If <code>object[methodName]</code> is not a function, an error is thrown.</li>
<li><code>implementation</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type">&#x3C;Function></a> | <a href="https://tc39.es/ecma262/#sec-async-function-constructor" class="type">&#x3C;AsyncFunction></a> An optional function used as the
mock implementation for <code>object[methodName]</code>. <strong>Default:</strong> The original method
specified by <code>object[methodName]</code>.</li>
<li><code>options</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type">&#x3C;Object></a> Optional configuration options for the mock method. The
following properties are supported:
<ul>
<li><code>getter</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type">&#x3C;boolean></a> If <code>true</code>, <code>object[methodName]</code> is treated as a getter.
This option cannot be used with the <code>setter</code> option. <strong>Default:</strong> false.</li>
<li><code>setter</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type">&#x3C;boolean></a> If <code>true</code>, <code>object[methodName]</code> is treated as a setter.
This option cannot be used with the <code>getter</code> option. <strong>Default:</strong> false.</li>
<li><code>times</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type">&#x3C;integer></a> The number of times that the mock will use the behavior of
<code>implementation</code>. Once the mocked method has been called <code>times</code> times, it
will automatically restore the original behavior. This value must be an
integer greater than zero. <strong>Default:</strong> <code>Infinity</code>.</li>
</ul>
</li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Proxy" class="type">&#x3C;Proxy></a> The mocked method. The mocked method contains a special
<code>mock</code> property, which is an instance of <a href="#class-mockfunctioncontext"><code>MockFunctionContext</code></a>, and can
be used for inspecting and changing the behavior of the mocked method.</li>
</ul>
<p>This function is used to create a mock on an existing object method. The
following example demonstrates how a mock is created on an existing object
method.</p>
<pre><code class="language-js"><span class="hljs-title function_">test</span>(<span class="hljs-string">'spies on an object method'</span>, <span class="hljs-function">(<span class="hljs-params">t</span>) =></span> {
  <span class="hljs-keyword">const</span> number = {
    <span class="hljs-attr">value</span>: <span class="hljs-number">5</span>,
    <span class="hljs-title function_">subtract</span>(<span class="hljs-params">a</span>) {
      <span class="hljs-keyword">return</span> <span class="hljs-variable language_">this</span>.<span class="hljs-property">value</span> - a;
    },
  };

  t.<span class="hljs-property">mock</span>.<span class="hljs-title function_">method</span>(number, <span class="hljs-string">'subtract'</span>);
  assert.<span class="hljs-title function_">strictEqual</span>(number.<span class="hljs-property">subtract</span>.<span class="hljs-property">mock</span>.<span class="hljs-title function_">callCount</span>(), <span class="hljs-number">0</span>);
  assert.<span class="hljs-title function_">strictEqual</span>(number.<span class="hljs-title function_">subtract</span>(<span class="hljs-number">3</span>), <span class="hljs-number">2</span>);
  assert.<span class="hljs-title function_">strictEqual</span>(number.<span class="hljs-property">subtract</span>.<span class="hljs-property">mock</span>.<span class="hljs-title function_">callCount</span>(), <span class="hljs-number">1</span>);

  <span class="hljs-keyword">const</span> call = number.<span class="hljs-property">subtract</span>.<span class="hljs-property">mock</span>.<span class="hljs-property">calls</span>[<span class="hljs-number">0</span>];

  assert.<span class="hljs-title function_">deepStrictEqual</span>(call.<span class="hljs-property">arguments</span>, [<span class="hljs-number">3</span>]);
  assert.<span class="hljs-title function_">strictEqual</span>(call.<span class="hljs-property">result</span>, <span class="hljs-number">2</span>);
  assert.<span class="hljs-title function_">strictEqual</span>(call.<span class="hljs-property">error</span>, <span class="hljs-literal">undefined</span>);
  assert.<span class="hljs-title function_">strictEqual</span>(call.<span class="hljs-property">target</span>, <span class="hljs-literal">undefined</span>);
  assert.<span class="hljs-title function_">strictEqual</span>(call.<span class="hljs-property">this</span>, number);
});</code> <button class="copy-button">copy</button></pre>
<h4><code>mock.module(specifier[, options])</code><span><a class="mark" href="#mockmodulespecifier-options" id="mockmodulespecifier-options">#</a></span><a aria-hidden="true" class="legacy" id="test_mock_module_specifier_options"></a></h4>
<div class="api_metadata">
<span>Added in: v22.3.0</span>
</div>
<p></p><div class="api_stability api_stability_1"><a href="documentation.html#stability-index">Stability: 1</a>.0 - Early development</div><p></p>
<ul>
<li><code>specifier</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type">&#x3C;string></a> | <a href="url.html#the-whatwg-url-api" class="type">&#x3C;URL></a> A string identifying the module to mock.</li>
<li><code>options</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type">&#x3C;Object></a> Optional configuration options for the mock module. The
following properties are supported:
<ul>
<li><code>cache</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type">&#x3C;boolean></a> If <code>false</code>, each call to <code>require()</code> or <code>import()</code>
generates a new mock module. If <code>true</code>, subsequent calls will return the same
module mock, and the mock module is inserted into the CommonJS cache.
<strong>Default:</strong> false.</li>
<li><code>defaultExport</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type">&#x3C;any></a> An optional value used as the mocked module's default
export. If this value is not provided, ESM mocks do not include a default
export. If the mock is a CommonJS or builtin module, this setting is used as
the value of <code>module.exports</code>. If this value is not provided, CJS and builtin
mocks use an empty object as the value of <code>module.exports</code>.</li>
<li><code>namedExports</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type">&#x3C;Object></a> An optional object whose keys and values are used to
create the named exports of the mock module. If the mock is a CommonJS or
builtin module, these values are copied onto <code>module.exports</code>. Therefore, if a
mock is created with both named exports and a non-object default export, the
mock will throw an exception when used as a CJS or builtin module.</li>
</ul>
</li>
<li>Returns: <a href="test.html#class-mockmodulecontext" class="type">&#x3C;MockModuleContext></a> An object that can be used to manipulate the mock.</li>
</ul>
<p>This function is used to mock the exports of ECMAScript modules, CommonJS
modules, and Node.js builtin modules. Any references to the original module
prior to mocking are not impacted. In order to enable module mocking, Node.js must
be started with the <a href="cli.html#--experimental-test-module-mocks"><code>--experimental-test-module-mocks</code></a> command-line flag.</p>
<p>The following example demonstrates how a mock is created for a module.</p>
<pre><code class="language-js"><span class="hljs-title function_">test</span>(<span class="hljs-string">'mocks a builtin module in both module systems'</span>, <span class="hljs-title function_">async</span> (t) => {
  <span class="hljs-comment">// Create a mock of 'node:readline' with a named export named 'fn', which</span>
  <span class="hljs-comment">// does not exist in the original 'node:readline' module.</span>
  <span class="hljs-keyword">const</span> mock = t.<span class="hljs-property">mock</span>.<span class="hljs-title function_">module</span>(<span class="hljs-string">'node:readline'</span>, {
    <span class="hljs-attr">namedExports</span>: { <span class="hljs-title function_">fn</span>(<span class="hljs-params"></span>) { <span class="hljs-keyword">return</span> <span class="hljs-number">42</span>; } },
  });

  <span class="hljs-keyword">let</span> esmImpl = <span class="hljs-keyword">await</span> <span class="hljs-keyword">import</span>(<span class="hljs-string">'node:readline'</span>);
  <span class="hljs-keyword">let</span> cjsImpl = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:readline'</span>);

  <span class="hljs-comment">// cursorTo() is an export of the original 'node:readline' module.</span>
  assert.<span class="hljs-title function_">strictEqual</span>(esmImpl.<span class="hljs-property">cursorTo</span>, <span class="hljs-literal">undefined</span>);
  assert.<span class="hljs-title function_">strictEqual</span>(cjsImpl.<span class="hljs-property">cursorTo</span>, <span class="hljs-literal">undefined</span>);
  assert.<span class="hljs-title function_">strictEqual</span>(esmImpl.<span class="hljs-title function_">fn</span>(), <span class="hljs-number">42</span>);
  assert.<span class="hljs-title function_">strictEqual</span>(cjsImpl.<span class="hljs-title function_">fn</span>(), <span class="hljs-number">42</span>);

  mock.<span class="hljs-title function_">restore</span>();

  <span class="hljs-comment">// The mock is restored, so the original builtin module is returned.</span>
  esmImpl = <span class="hljs-keyword">await</span> <span class="hljs-keyword">import</span>(<span class="hljs-string">'node:readline'</span>);
  cjsImpl = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:readline'</span>);

  assert.<span class="hljs-title function_">strictEqual</span>(<span class="hljs-keyword">typeof</span> esmImpl.<span class="hljs-property">cursorTo</span>, <span class="hljs-string">'function'</span>);
  assert.<span class="hljs-title function_">strictEqual</span>(<span class="hljs-keyword">typeof</span> cjsImpl.<span class="hljs-property">cursorTo</span>, <span class="hljs-string">'function'</span>);
  assert.<span class="hljs-title function_">strictEqual</span>(esmImpl.<span class="hljs-property">fn</span>, <span class="hljs-literal">undefined</span>);
  assert.<span class="hljs-title function_">strictEqual</span>(cjsImpl.<span class="hljs-property">fn</span>, <span class="hljs-literal">undefined</span>);
});</code> <button class="copy-button">copy</button></pre>
<h4><code>mock.reset()</code><span><a class="mark" href="#mockreset" id="mockreset">#</a></span><a aria-hidden="true" class="legacy" id="test_mock_reset"></a></h4>
<div class="api_metadata">
<span>Added in: v19.1.0, v18.13.0</span>
</div>
<p>This function restores the default behavior of all mocks that were previously
created by this <code>MockTracker</code> and disassociates the mocks from the
<code>MockTracker</code> instance. Once disassociated, the mocks can still be used, but the
<code>MockTracker</code> instance can no longer be used to reset their behavior or
otherwise interact with them.</p>
<p>After each test completes, this function is called on the test context's
<code>MockTracker</code>. If the global <code>MockTracker</code> is used extensively, calling this
function manually is recommended.</p>
<h4><code>mock.restoreAll()</code><span><a class="mark" href="#mockrestoreall" id="mockrestoreall">#</a></span><a aria-hidden="true" class="legacy" id="test_mock_restoreall"></a></h4>
<div class="api_metadata">
<span>Added in: v19.1.0, v18.13.0</span>
</div>
<p>This function restores the default behavior of all mocks that were previously
created by this <code>MockTracker</code>. Unlike <code>mock.reset()</code>, <code>mock.restoreAll()</code> does
not disassociate the mocks from the <code>MockTracker</code> instance.</p>
<h4><code>mock.setter(object, methodName[, implementation][, options])</code><span><a class="mark" href="#mocksetterobject-methodname-implementation-options" id="mocksetterobject-methodname-implementation-options">#</a></span><a aria-hidden="true" class="legacy" id="test_mock_setter_object_methodname_implementation_options"></a></h4>
<div class="api_metadata">
<span>Added in: v19.3.0, v18.13.0</span>
</div>
<p>This function is syntax sugar for <a href="#mockmethodobject-methodname-implementation-options"><code>MockTracker.method</code></a> with <code>options.setter</code>
set to <code>true</code>.</p>
</section><section><h3>Class: <code>MockTimers</code><span><a class="mark" href="#class-mocktimers" id="class-mocktimers">#</a></span><a aria-hidden="true" class="legacy" id="test_class_mocktimers"></a></h3>
<div class="api_metadata">
<span>Added in: v20.4.0, v18.19.0</span>
</div>
<p></p><div class="api_stability api_stability_1"><a href="documentation.html#stability-index">Stability: 1</a> - Experimental</div><p></p>
<p>Mocking timers is a technique commonly used in software testing to simulate and
control the behavior of timers, such as <code>setInterval</code> and <code>setTimeout</code>,
without actually waiting for the specified time intervals.</p>
<p>MockTimers is also able to mock the <code>Date</code> object.</p>
<p>The <a href="#class-mocktracker"><code>MockTracker</code></a> provides a top-level <code>timers</code> export
which is a <code>MockTimers</code> instance.</p>
<h4><code>timers.enable([enableOptions])</code><span><a class="mark" href="#timersenableenableoptions" id="timersenableenableoptions">#</a></span><a aria-hidden="true" class="legacy" id="test_timers_enable_enableoptions"></a></h4>
<div class="api_metadata">
<details class="changelog"><summary>History</summary>
<table>
<tbody><tr><th>Version</th><th>Changes</th></tr>
<tr><td>v21.2.0, v20.11.0</td>
<td><p>Updated parameters to be an option object with available APIs and the default initial epoch.</p></td></tr>
<tr><td>v20.4.0, v18.19.0</td>
<td><p><span>Added in: v20.4.0, v18.19.0</span></p></td></tr>
</tbody></table>
</details>
</div>
<p>Enables timer mocking for the specified timers.</p>
<ul>
<li><code>enableOptions</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type">&#x3C;Object></a> Optional configuration options for enabling timer
mocking. The following properties are supported:
<ul>
<li><code>apis</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array" class="type">&#x3C;Array></a> An optional array containing the timers to mock.
The currently supported timer values are <code>'setInterval'</code>, <code>'setTimeout'</code>, <code>'setImmediate'</code>,
and <code>'Date'</code>. <strong>Default:</strong> <code>['setInterval', 'setTimeout', 'setImmediate', 'Date']</code>.
If no array is provided, all time related APIs (<code>'setInterval'</code>, <code>'clearInterval'</code>,
<code>'setTimeout'</code>, <code>'clearTimeout'</code>, <code>'setImmediate'</code>, <code>'clearImmediate'</code>, and
<code>'Date'</code>) will be mocked by default.</li>
<li><code>now</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type">&#x3C;number></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Date" class="type">&#x3C;Date></a> An optional number or Date object representing the
initial time (in milliseconds) to use as the value
for <code>Date.now()</code>. <strong>Default:</strong> <code>0</code>.</li>
</ul>
</li>
</ul>
<p><strong>Note:</strong> When you enable mocking for a specific timer, its associated
clear function will also be implicitly mocked.</p>
<p><strong>Note:</strong> Mocking <code>Date</code> will affect the behavior of the mocked timers
as they use the same internal clock.</p>
<p>Example usage without setting initial time:</p>

<pre class="with-46-chars"><input class="js-flavor-toggle" type="checkbox" checked aria-label="Show modern ES modules syntax"><code class="language-js mjs"><span class="hljs-keyword">import</span> { mock } <span class="hljs-keyword">from</span> <span class="hljs-string">'node:test'</span>;
mock.<span class="hljs-property">timers</span>.<span class="hljs-title function_">enable</span>({ <span class="hljs-attr">apis</span>: [<span class="hljs-string">'setInterval'</span>] });</code><code class="language-js cjs"><span class="hljs-keyword">const</span> { mock } = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:test'</span>);
mock.<span class="hljs-property">timers</span>.<span class="hljs-title function_">enable</span>({ <span class="hljs-attr">apis</span>: [<span class="hljs-string">'setInterval'</span>] });</code><button class="copy-button">copy</button></pre>
<p>The above example enables mocking for the <code>setInterval</code> timer and
implicitly mocks the <code>clearInterval</code> function. Only the <code>setInterval</code>
and <code>clearInterval</code> functions from <a href="./timers.html">node:timers</a>,
<a href="./timers.html#timers-promises-api">node:timers/promises</a>, and
<code>globalThis</code> will be mocked.</p>
<p>Example usage with initial time set</p>

<pre class="with-50-chars"><input class="js-flavor-toggle" type="checkbox" checked aria-label="Show modern ES modules syntax"><code class="language-js mjs"><span class="hljs-keyword">import</span> { mock } <span class="hljs-keyword">from</span> <span class="hljs-string">'node:test'</span>;
mock.<span class="hljs-property">timers</span>.<span class="hljs-title function_">enable</span>({ <span class="hljs-attr">apis</span>: [<span class="hljs-string">'Date'</span>], <span class="hljs-attr">now</span>: <span class="hljs-number">1000</span> });</code><code class="language-js cjs"><span class="hljs-keyword">const</span> { mock } = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:test'</span>);
mock.<span class="hljs-property">timers</span>.<span class="hljs-title function_">enable</span>({ <span class="hljs-attr">apis</span>: [<span class="hljs-string">'Date'</span>], <span class="hljs-attr">now</span>: <span class="hljs-number">1000</span> });</code><button class="copy-button">copy</button></pre>
<p>Example usage with initial Date object as time set</p>

<pre class="with-56-chars"><input class="js-flavor-toggle" type="checkbox" checked aria-label="Show modern ES modules syntax"><code class="language-js mjs"><span class="hljs-keyword">import</span> { mock } <span class="hljs-keyword">from</span> <span class="hljs-string">'node:test'</span>;
mock.<span class="hljs-property">timers</span>.<span class="hljs-title function_">enable</span>({ <span class="hljs-attr">apis</span>: [<span class="hljs-string">'Date'</span>], <span class="hljs-attr">now</span>: <span class="hljs-keyword">new</span> <span class="hljs-title class_">Date</span>() });</code><code class="language-js cjs"><span class="hljs-keyword">const</span> { mock } = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:test'</span>);
mock.<span class="hljs-property">timers</span>.<span class="hljs-title function_">enable</span>({ <span class="hljs-attr">apis</span>: [<span class="hljs-string">'Date'</span>], <span class="hljs-attr">now</span>: <span class="hljs-keyword">new</span> <span class="hljs-title class_">Date</span>() });</code><button class="copy-button">copy</button></pre>
<p>Alternatively, if you call <code>mock.timers.enable()</code> without any parameters:</p>
<p>All timers (<code>'setInterval'</code>, <code>'clearInterval'</code>, <code>'setTimeout'</code>, <code>'clearTimeout'</code>,
<code>'setImmediate'</code>, and <code>'clearImmediate'</code>) will be mocked. The <code>setInterval</code>,
<code>clearInterval</code>, <code>setTimeout</code>, <code>clearTimeout</code>, <code>setImmediate</code>, and
<code>clearImmediate</code> functions from <code>node:timers</code>, <code>node:timers/promises</code>, and
<code>globalThis</code> will be mocked. As well as the global <code>Date</code> object.</p>
<h4><code>timers.reset()</code><span><a class="mark" href="#timersreset" id="timersreset">#</a></span><a aria-hidden="true" class="legacy" id="test_timers_reset"></a></h4>
<div class="api_metadata">
<span>Added in: v20.4.0, v18.19.0</span>
</div>
<p>This function restores the default behavior of all mocks that were previously
created by this  <code>MockTimers</code> instance and disassociates the mocks
from the  <code>MockTracker</code> instance.</p>
<p><strong>Note:</strong> After each test completes, this function is called on
the test context's  <code>MockTracker</code>.</p>

<pre class="with-38-chars"><input class="js-flavor-toggle" type="checkbox" checked aria-label="Show modern ES modules syntax"><code class="language-js mjs"><span class="hljs-keyword">import</span> { mock } <span class="hljs-keyword">from</span> <span class="hljs-string">'node:test'</span>;
mock.<span class="hljs-property">timers</span>.<span class="hljs-title function_">reset</span>();</code><code class="language-js cjs"><span class="hljs-keyword">const</span> { mock } = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:test'</span>);
mock.<span class="hljs-property">timers</span>.<span class="hljs-title function_">reset</span>();</code><button class="copy-button">copy</button></pre>
<h4><code>timers[Symbol.dispose]()</code><span><a class="mark" href="#timerssymboldispose" id="timerssymboldispose">#</a></span><a aria-hidden="true" class="legacy" id="test_timers_symbol_dispose"></a></h4>
<p>Calls <code>timers.reset()</code>.</p>
<h4><code>timers.tick([milliseconds])</code><span><a class="mark" href="#timerstickmilliseconds" id="timerstickmilliseconds">#</a></span><a aria-hidden="true" class="legacy" id="test_timers_tick_milliseconds"></a></h4>
<div class="api_metadata">
<span>Added in: v20.4.0, v18.19.0</span>
</div>
<p>Advances time for all mocked timers.</p>
<ul>
<li><code>milliseconds</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type">&#x3C;number></a> The amount of time, in milliseconds,
to advance the timers. <strong>Default:</strong> <code>1</code>.</li>
</ul>
<p><strong>Note:</strong> This diverges from how <code>setTimeout</code> in Node.js behaves and accepts
only positive numbers. In Node.js, <code>setTimeout</code> with negative numbers is
only supported for web compatibility reasons.</p>
<p>The following example mocks a <code>setTimeout</code> function and
by using <code>.tick</code> advances in
time triggering all pending timers.</p>

<pre class="with-38-chars"><input class="js-flavor-toggle" type="checkbox" checked aria-label="Show modern ES modules syntax"><code class="language-js mjs"><span class="hljs-keyword">import</span> assert <span class="hljs-keyword">from</span> <span class="hljs-string">'node:assert'</span>;
<span class="hljs-keyword">import</span> { test } <span class="hljs-keyword">from</span> <span class="hljs-string">'node:test'</span>;

<span class="hljs-title function_">test</span>(<span class="hljs-string">'mocks setTimeout to be executed synchronously without having to actually wait for it'</span>, <span class="hljs-function">(<span class="hljs-params">context</span>) =></span> {
  <span class="hljs-keyword">const</span> fn = context.<span class="hljs-property">mock</span>.<span class="hljs-title function_">fn</span>();

  context.<span class="hljs-property">mock</span>.<span class="hljs-property">timers</span>.<span class="hljs-title function_">enable</span>({ <span class="hljs-attr">apis</span>: [<span class="hljs-string">'setTimeout'</span>] });

  <span class="hljs-built_in">setTimeout</span>(fn, <span class="hljs-number">9999</span>);

  assert.<span class="hljs-title function_">strictEqual</span>(fn.<span class="hljs-property">mock</span>.<span class="hljs-title function_">callCount</span>(), <span class="hljs-number">0</span>);

  <span class="hljs-comment">// Advance in time</span>
  context.<span class="hljs-property">mock</span>.<span class="hljs-property">timers</span>.<span class="hljs-title function_">tick</span>(<span class="hljs-number">9999</span>);

  assert.<span class="hljs-title function_">strictEqual</span>(fn.<span class="hljs-property">mock</span>.<span class="hljs-title function_">callCount</span>(), <span class="hljs-number">1</span>);
});</code><code class="language-js cjs"><span class="hljs-keyword">const</span> assert = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:assert'</span>);
<span class="hljs-keyword">const</span> { test } = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:test'</span>);

<span class="hljs-title function_">test</span>(<span class="hljs-string">'mocks setTimeout to be executed synchronously without having to actually wait for it'</span>, <span class="hljs-function">(<span class="hljs-params">context</span>) =></span> {
  <span class="hljs-keyword">const</span> fn = context.<span class="hljs-property">mock</span>.<span class="hljs-title function_">fn</span>();
  context.<span class="hljs-property">mock</span>.<span class="hljs-property">timers</span>.<span class="hljs-title function_">enable</span>({ <span class="hljs-attr">apis</span>: [<span class="hljs-string">'setTimeout'</span>] });

  <span class="hljs-built_in">setTimeout</span>(fn, <span class="hljs-number">9999</span>);
  assert.<span class="hljs-title function_">strictEqual</span>(fn.<span class="hljs-property">mock</span>.<span class="hljs-title function_">callCount</span>(), <span class="hljs-number">0</span>);

  <span class="hljs-comment">// Advance in time</span>
  context.<span class="hljs-property">mock</span>.<span class="hljs-property">timers</span>.<span class="hljs-title function_">tick</span>(<span class="hljs-number">9999</span>);

  assert.<span class="hljs-title function_">strictEqual</span>(fn.<span class="hljs-property">mock</span>.<span class="hljs-title function_">callCount</span>(), <span class="hljs-number">1</span>);
});</code><button class="copy-button">copy</button></pre>
<p>Alternatively, the <code>.tick</code> function can be called many times</p>

<pre class="with-38-chars"><input class="js-flavor-toggle" type="checkbox" checked aria-label="Show modern ES modules syntax"><code class="language-js mjs"><span class="hljs-keyword">import</span> assert <span class="hljs-keyword">from</span> <span class="hljs-string">'node:assert'</span>;
<span class="hljs-keyword">import</span> { test } <span class="hljs-keyword">from</span> <span class="hljs-string">'node:test'</span>;

<span class="hljs-title function_">test</span>(<span class="hljs-string">'mocks setTimeout to be executed synchronously without having to actually wait for it'</span>, <span class="hljs-function">(<span class="hljs-params">context</span>) =></span> {
  <span class="hljs-keyword">const</span> fn = context.<span class="hljs-property">mock</span>.<span class="hljs-title function_">fn</span>();
  context.<span class="hljs-property">mock</span>.<span class="hljs-property">timers</span>.<span class="hljs-title function_">enable</span>({ <span class="hljs-attr">apis</span>: [<span class="hljs-string">'setTimeout'</span>] });
  <span class="hljs-keyword">const</span> nineSecs = <span class="hljs-number">9000</span>;
  <span class="hljs-built_in">setTimeout</span>(fn, nineSecs);

  <span class="hljs-keyword">const</span> threeSeconds = <span class="hljs-number">3000</span>;
  context.<span class="hljs-property">mock</span>.<span class="hljs-property">timers</span>.<span class="hljs-title function_">tick</span>(threeSeconds);
  context.<span class="hljs-property">mock</span>.<span class="hljs-property">timers</span>.<span class="hljs-title function_">tick</span>(threeSeconds);
  context.<span class="hljs-property">mock</span>.<span class="hljs-property">timers</span>.<span class="hljs-title function_">tick</span>(threeSeconds);

  assert.<span class="hljs-title function_">strictEqual</span>(fn.<span class="hljs-property">mock</span>.<span class="hljs-title function_">callCount</span>(), <span class="hljs-number">1</span>);
});</code><code class="language-js cjs"><span class="hljs-keyword">const</span> assert = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:assert'</span>);
<span class="hljs-keyword">const</span> { test } = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:test'</span>);

<span class="hljs-title function_">test</span>(<span class="hljs-string">'mocks setTimeout to be executed synchronously without having to actually wait for it'</span>, <span class="hljs-function">(<span class="hljs-params">context</span>) =></span> {
  <span class="hljs-keyword">const</span> fn = context.<span class="hljs-property">mock</span>.<span class="hljs-title function_">fn</span>();
  context.<span class="hljs-property">mock</span>.<span class="hljs-property">timers</span>.<span class="hljs-title function_">enable</span>({ <span class="hljs-attr">apis</span>: [<span class="hljs-string">'setTimeout'</span>] });
  <span class="hljs-keyword">const</span> nineSecs = <span class="hljs-number">9000</span>;
  <span class="hljs-built_in">setTimeout</span>(fn, nineSecs);

  <span class="hljs-keyword">const</span> threeSeconds = <span class="hljs-number">3000</span>;
  context.<span class="hljs-property">mock</span>.<span class="hljs-property">timers</span>.<span class="hljs-title function_">tick</span>(threeSeconds);
  context.<span class="hljs-property">mock</span>.<span class="hljs-property">timers</span>.<span class="hljs-title function_">tick</span>(threeSeconds);
  context.<span class="hljs-property">mock</span>.<span class="hljs-property">timers</span>.<span class="hljs-title function_">tick</span>(threeSeconds);

  assert.<span class="hljs-title function_">strictEqual</span>(fn.<span class="hljs-property">mock</span>.<span class="hljs-title function_">callCount</span>(), <span class="hljs-number">1</span>);
});</code><button class="copy-button">copy</button></pre>
<p>Advancing time using <code>.tick</code> will also advance the time for any <code>Date</code> object
created after the mock was enabled (if <code>Date</code> was also set to be mocked).</p>

<pre class="with-38-chars"><input class="js-flavor-toggle" type="checkbox" checked aria-label="Show modern ES modules syntax"><code class="language-js mjs"><span class="hljs-keyword">import</span> assert <span class="hljs-keyword">from</span> <span class="hljs-string">'node:assert'</span>;
<span class="hljs-keyword">import</span> { test } <span class="hljs-keyword">from</span> <span class="hljs-string">'node:test'</span>;

<span class="hljs-title function_">test</span>(<span class="hljs-string">'mocks setTimeout to be executed synchronously without having to actually wait for it'</span>, <span class="hljs-function">(<span class="hljs-params">context</span>) =></span> {
  <span class="hljs-keyword">const</span> fn = context.<span class="hljs-property">mock</span>.<span class="hljs-title function_">fn</span>();

  context.<span class="hljs-property">mock</span>.<span class="hljs-property">timers</span>.<span class="hljs-title function_">enable</span>({ <span class="hljs-attr">apis</span>: [<span class="hljs-string">'setTimeout'</span>, <span class="hljs-string">'Date'</span>] });
  <span class="hljs-built_in">setTimeout</span>(fn, <span class="hljs-number">9999</span>);

  assert.<span class="hljs-title function_">strictEqual</span>(fn.<span class="hljs-property">mock</span>.<span class="hljs-title function_">callCount</span>(), <span class="hljs-number">0</span>);
  assert.<span class="hljs-title function_">strictEqual</span>(<span class="hljs-title class_">Date</span>.<span class="hljs-title function_">now</span>(), <span class="hljs-number">0</span>);

  <span class="hljs-comment">// Advance in time</span>
  context.<span class="hljs-property">mock</span>.<span class="hljs-property">timers</span>.<span class="hljs-title function_">tick</span>(<span class="hljs-number">9999</span>);
  assert.<span class="hljs-title function_">strictEqual</span>(fn.<span class="hljs-property">mock</span>.<span class="hljs-title function_">callCount</span>(), <span class="hljs-number">1</span>);
  assert.<span class="hljs-title function_">strictEqual</span>(<span class="hljs-title class_">Date</span>.<span class="hljs-title function_">now</span>(), <span class="hljs-number">9999</span>);
});</code><code class="language-js cjs"><span class="hljs-keyword">const</span> assert = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:assert'</span>);
<span class="hljs-keyword">const</span> { test } = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:test'</span>);

<span class="hljs-title function_">test</span>(<span class="hljs-string">'mocks setTimeout to be executed synchronously without having to actually wait for it'</span>, <span class="hljs-function">(<span class="hljs-params">context</span>) =></span> {
  <span class="hljs-keyword">const</span> fn = context.<span class="hljs-property">mock</span>.<span class="hljs-title function_">fn</span>();
  context.<span class="hljs-property">mock</span>.<span class="hljs-property">timers</span>.<span class="hljs-title function_">enable</span>({ <span class="hljs-attr">apis</span>: [<span class="hljs-string">'setTimeout'</span>, <span class="hljs-string">'Date'</span>] });

  <span class="hljs-built_in">setTimeout</span>(fn, <span class="hljs-number">9999</span>);
  assert.<span class="hljs-title function_">strictEqual</span>(fn.<span class="hljs-property">mock</span>.<span class="hljs-title function_">callCount</span>(), <span class="hljs-number">0</span>);
  assert.<span class="hljs-title function_">strictEqual</span>(<span class="hljs-title class_">Date</span>.<span class="hljs-title function_">now</span>(), <span class="hljs-number">0</span>);

  <span class="hljs-comment">// Advance in time</span>
  context.<span class="hljs-property">mock</span>.<span class="hljs-property">timers</span>.<span class="hljs-title function_">tick</span>(<span class="hljs-number">9999</span>);
  assert.<span class="hljs-title function_">strictEqual</span>(fn.<span class="hljs-property">mock</span>.<span class="hljs-title function_">callCount</span>(), <span class="hljs-number">1</span>);
  assert.<span class="hljs-title function_">strictEqual</span>(<span class="hljs-title class_">Date</span>.<span class="hljs-title function_">now</span>(), <span class="hljs-number">9999</span>);
});</code><button class="copy-button">copy</button></pre>
<h5>Using clear functions<span><a class="mark" href="#using-clear-functions" id="using-clear-functions">#</a></span><a aria-hidden="true" class="legacy" id="test_using_clear_functions"></a></h5>
<p>As mentioned, all clear functions from timers (<code>clearTimeout</code>, <code>clearInterval</code>,and
<code>clearImmediate</code>) are implicitly mocked. Take a look at this example using <code>setTimeout</code>:</p>

<pre class="with-38-chars"><input class="js-flavor-toggle" type="checkbox" checked aria-label="Show modern ES modules syntax"><code class="language-js mjs"><span class="hljs-keyword">import</span> assert <span class="hljs-keyword">from</span> <span class="hljs-string">'node:assert'</span>;
<span class="hljs-keyword">import</span> { test } <span class="hljs-keyword">from</span> <span class="hljs-string">'node:test'</span>;

<span class="hljs-title function_">test</span>(<span class="hljs-string">'mocks setTimeout to be executed synchronously without having to actually wait for it'</span>, <span class="hljs-function">(<span class="hljs-params">context</span>) =></span> {
  <span class="hljs-keyword">const</span> fn = context.<span class="hljs-property">mock</span>.<span class="hljs-title function_">fn</span>();

  <span class="hljs-comment">// Optionally choose what to mock</span>
  context.<span class="hljs-property">mock</span>.<span class="hljs-property">timers</span>.<span class="hljs-title function_">enable</span>({ <span class="hljs-attr">apis</span>: [<span class="hljs-string">'setTimeout'</span>] });
  <span class="hljs-keyword">const</span> id = <span class="hljs-built_in">setTimeout</span>(fn, <span class="hljs-number">9999</span>);

  <span class="hljs-comment">// Implicitly mocked as well</span>
  <span class="hljs-built_in">clearTimeout</span>(id);
  context.<span class="hljs-property">mock</span>.<span class="hljs-property">timers</span>.<span class="hljs-title function_">tick</span>(<span class="hljs-number">9999</span>);

  <span class="hljs-comment">// As that setTimeout was cleared the mock function will never be called</span>
  assert.<span class="hljs-title function_">strictEqual</span>(fn.<span class="hljs-property">mock</span>.<span class="hljs-title function_">callCount</span>(), <span class="hljs-number">0</span>);
});</code><code class="language-js cjs"><span class="hljs-keyword">const</span> assert = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:assert'</span>);
<span class="hljs-keyword">const</span> { test } = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:test'</span>);

<span class="hljs-title function_">test</span>(<span class="hljs-string">'mocks setTimeout to be executed synchronously without having to actually wait for it'</span>, <span class="hljs-function">(<span class="hljs-params">context</span>) =></span> {
  <span class="hljs-keyword">const</span> fn = context.<span class="hljs-property">mock</span>.<span class="hljs-title function_">fn</span>();

  <span class="hljs-comment">// Optionally choose what to mock</span>
  context.<span class="hljs-property">mock</span>.<span class="hljs-property">timers</span>.<span class="hljs-title function_">enable</span>({ <span class="hljs-attr">apis</span>: [<span class="hljs-string">'setTimeout'</span>] });
  <span class="hljs-keyword">const</span> id = <span class="hljs-built_in">setTimeout</span>(fn, <span class="hljs-number">9999</span>);

  <span class="hljs-comment">// Implicitly mocked as well</span>
  <span class="hljs-built_in">clearTimeout</span>(id);
  context.<span class="hljs-property">mock</span>.<span class="hljs-property">timers</span>.<span class="hljs-title function_">tick</span>(<span class="hljs-number">9999</span>);

  <span class="hljs-comment">// As that setTimeout was cleared the mock function will never be called</span>
  assert.<span class="hljs-title function_">strictEqual</span>(fn.<span class="hljs-property">mock</span>.<span class="hljs-title function_">callCount</span>(), <span class="hljs-number">0</span>);
});</code><button class="copy-button">copy</button></pre>
<h5>Working with Node.js timers modules<span><a class="mark" href="#working-with-nodejs-timers-modules" id="working-with-nodejs-timers-modules">#</a></span><a aria-hidden="true" class="legacy" id="test_working_with_node_js_timers_modules"></a></h5>
<p>Once you enable mocking timers, <a href="./timers.html">node:timers</a>,
<a href="./timers.html#timers-promises-api">node:timers/promises</a> modules,
and timers from the Node.js global context are enabled:</p>
<p><strong>Note:</strong> Destructuring functions such as
<code>import { setTimeout } from 'node:timers'</code> is currently
not supported by this API.</p>

<pre class="with-38-chars"><input class="js-flavor-toggle" type="checkbox" checked aria-label="Show modern ES modules syntax"><code class="language-js mjs"><span class="hljs-keyword">import</span> assert <span class="hljs-keyword">from</span> <span class="hljs-string">'node:assert'</span>;
<span class="hljs-keyword">import</span> { test } <span class="hljs-keyword">from</span> <span class="hljs-string">'node:test'</span>;
<span class="hljs-keyword">import</span> nodeTimers <span class="hljs-keyword">from</span> <span class="hljs-string">'node:timers'</span>;
<span class="hljs-keyword">import</span> nodeTimersPromises <span class="hljs-keyword">from</span> <span class="hljs-string">'node:timers/promises'</span>;

<span class="hljs-title function_">test</span>(<span class="hljs-string">'mocks setTimeout to be executed synchronously without having to actually wait for it'</span>, <span class="hljs-title function_">async</span> (context) => {
  <span class="hljs-keyword">const</span> globalTimeoutObjectSpy = context.<span class="hljs-property">mock</span>.<span class="hljs-title function_">fn</span>();
  <span class="hljs-keyword">const</span> nodeTimerSpy = context.<span class="hljs-property">mock</span>.<span class="hljs-title function_">fn</span>();
  <span class="hljs-keyword">const</span> nodeTimerPromiseSpy = context.<span class="hljs-property">mock</span>.<span class="hljs-title function_">fn</span>();

  <span class="hljs-comment">// Optionally choose what to mock</span>
  context.<span class="hljs-property">mock</span>.<span class="hljs-property">timers</span>.<span class="hljs-title function_">enable</span>({ <span class="hljs-attr">apis</span>: [<span class="hljs-string">'setTimeout'</span>] });
  <span class="hljs-built_in">setTimeout</span>(globalTimeoutObjectSpy, <span class="hljs-number">9999</span>);
  nodeTimers.<span class="hljs-built_in">setTimeout</span>(nodeTimerSpy, <span class="hljs-number">9999</span>);

  <span class="hljs-keyword">const</span> promise = nodeTimersPromises.<span class="hljs-built_in">setTimeout</span>(<span class="hljs-number">9999</span>).<span class="hljs-title function_">then</span>(nodeTimerPromiseSpy);

  <span class="hljs-comment">// Advance in time</span>
  context.<span class="hljs-property">mock</span>.<span class="hljs-property">timers</span>.<span class="hljs-title function_">tick</span>(<span class="hljs-number">9999</span>);
  assert.<span class="hljs-title function_">strictEqual</span>(globalTimeoutObjectSpy.<span class="hljs-property">mock</span>.<span class="hljs-title function_">callCount</span>(), <span class="hljs-number">1</span>);
  assert.<span class="hljs-title function_">strictEqual</span>(nodeTimerSpy.<span class="hljs-property">mock</span>.<span class="hljs-title function_">callCount</span>(), <span class="hljs-number">1</span>);
  <span class="hljs-keyword">await</span> promise;
  assert.<span class="hljs-title function_">strictEqual</span>(nodeTimerPromiseSpy.<span class="hljs-property">mock</span>.<span class="hljs-title function_">callCount</span>(), <span class="hljs-number">1</span>);
});</code><code class="language-js cjs"><span class="hljs-keyword">const</span> assert = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:assert'</span>);
<span class="hljs-keyword">const</span> { test } = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:test'</span>);
<span class="hljs-keyword">const</span> nodeTimers = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:timers'</span>);
<span class="hljs-keyword">const</span> nodeTimersPromises = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:timers/promises'</span>);

<span class="hljs-title function_">test</span>(<span class="hljs-string">'mocks setTimeout to be executed synchronously without having to actually wait for it'</span>, <span class="hljs-title function_">async</span> (context) => {
  <span class="hljs-keyword">const</span> globalTimeoutObjectSpy = context.<span class="hljs-property">mock</span>.<span class="hljs-title function_">fn</span>();
  <span class="hljs-keyword">const</span> nodeTimerSpy = context.<span class="hljs-property">mock</span>.<span class="hljs-title function_">fn</span>();
  <span class="hljs-keyword">const</span> nodeTimerPromiseSpy = context.<span class="hljs-property">mock</span>.<span class="hljs-title function_">fn</span>();

  <span class="hljs-comment">// Optionally choose what to mock</span>
  context.<span class="hljs-property">mock</span>.<span class="hljs-property">timers</span>.<span class="hljs-title function_">enable</span>({ <span class="hljs-attr">apis</span>: [<span class="hljs-string">'setTimeout'</span>] });
  <span class="hljs-built_in">setTimeout</span>(globalTimeoutObjectSpy, <span class="hljs-number">9999</span>);
  nodeTimers.<span class="hljs-built_in">setTimeout</span>(nodeTimerSpy, <span class="hljs-number">9999</span>);

  <span class="hljs-keyword">const</span> promise = nodeTimersPromises.<span class="hljs-built_in">setTimeout</span>(<span class="hljs-number">9999</span>).<span class="hljs-title function_">then</span>(nodeTimerPromiseSpy);

  <span class="hljs-comment">// Advance in time</span>
  context.<span class="hljs-property">mock</span>.<span class="hljs-property">timers</span>.<span class="hljs-title function_">tick</span>(<span class="hljs-number">9999</span>);
  assert.<span class="hljs-title function_">strictEqual</span>(globalTimeoutObjectSpy.<span class="hljs-property">mock</span>.<span class="hljs-title function_">callCount</span>(), <span class="hljs-number">1</span>);
  assert.<span class="hljs-title function_">strictEqual</span>(nodeTimerSpy.<span class="hljs-property">mock</span>.<span class="hljs-title function_">callCount</span>(), <span class="hljs-number">1</span>);
  <span class="hljs-keyword">await</span> promise;
  assert.<span class="hljs-title function_">strictEqual</span>(nodeTimerPromiseSpy.<span class="hljs-property">mock</span>.<span class="hljs-title function_">callCount</span>(), <span class="hljs-number">1</span>);
});</code><button class="copy-button">copy</button></pre>
<p>In Node.js, <code>setInterval</code> from <a href="./timers.html#timers-promises-api">node:timers/promises</a>
is an <code>AsyncGenerator</code> and is also supported by this API:</p>

<pre class="with-38-chars"><input class="js-flavor-toggle" type="checkbox" checked aria-label="Show modern ES modules syntax"><code class="language-js mjs"><span class="hljs-keyword">import</span> assert <span class="hljs-keyword">from</span> <span class="hljs-string">'node:assert'</span>;
<span class="hljs-keyword">import</span> { test } <span class="hljs-keyword">from</span> <span class="hljs-string">'node:test'</span>;
<span class="hljs-keyword">import</span> nodeTimersPromises <span class="hljs-keyword">from</span> <span class="hljs-string">'node:timers/promises'</span>;
<span class="hljs-title function_">test</span>(<span class="hljs-string">'should tick five times testing a real use case'</span>, <span class="hljs-title function_">async</span> (context) => {
  context.<span class="hljs-property">mock</span>.<span class="hljs-property">timers</span>.<span class="hljs-title function_">enable</span>({ <span class="hljs-attr">apis</span>: [<span class="hljs-string">'setInterval'</span>] });

  <span class="hljs-keyword">const</span> expectedIterations = <span class="hljs-number">3</span>;
  <span class="hljs-keyword">const</span> interval = <span class="hljs-number">1000</span>;
  <span class="hljs-keyword">const</span> startedAt = <span class="hljs-title class_">Date</span>.<span class="hljs-title function_">now</span>();
  <span class="hljs-keyword">async</span> <span class="hljs-keyword">function</span> <span class="hljs-title function_">run</span>(<span class="hljs-params"></span>) {
    <span class="hljs-keyword">const</span> times = [];
    <span class="hljs-keyword">for</span> <span class="hljs-title function_">await</span> (<span class="hljs-keyword">const</span> time <span class="hljs-keyword">of</span> nodeTimersPromises.<span class="hljs-built_in">setInterval</span>(interval, startedAt)) {
      times.<span class="hljs-title function_">push</span>(time);
      <span class="hljs-keyword">if</span> (times.<span class="hljs-property">length</span> === expectedIterations) <span class="hljs-keyword">break</span>;
    }
    <span class="hljs-keyword">return</span> times;
  }

  <span class="hljs-keyword">const</span> r = <span class="hljs-title function_">run</span>();
  context.<span class="hljs-property">mock</span>.<span class="hljs-property">timers</span>.<span class="hljs-title function_">tick</span>(interval);
  context.<span class="hljs-property">mock</span>.<span class="hljs-property">timers</span>.<span class="hljs-title function_">tick</span>(interval);
  context.<span class="hljs-property">mock</span>.<span class="hljs-property">timers</span>.<span class="hljs-title function_">tick</span>(interval);

  <span class="hljs-keyword">const</span> timeResults = <span class="hljs-keyword">await</span> r;
  assert.<span class="hljs-title function_">strictEqual</span>(timeResults.<span class="hljs-property">length</span>, expectedIterations);
  <span class="hljs-keyword">for</span> (<span class="hljs-keyword">let</span> it = <span class="hljs-number">1</span>; it &#x3C; expectedIterations; it++) {
    assert.<span class="hljs-title function_">strictEqual</span>(timeResults[it - <span class="hljs-number">1</span>], startedAt + (interval * it));
  }
});</code><code class="language-js cjs"><span class="hljs-keyword">const</span> assert = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:assert'</span>);
<span class="hljs-keyword">const</span> { test } = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:test'</span>);
<span class="hljs-keyword">const</span> nodeTimersPromises = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:timers/promises'</span>);
<span class="hljs-title function_">test</span>(<span class="hljs-string">'should tick five times testing a real use case'</span>, <span class="hljs-title function_">async</span> (context) => {
  context.<span class="hljs-property">mock</span>.<span class="hljs-property">timers</span>.<span class="hljs-title function_">enable</span>({ <span class="hljs-attr">apis</span>: [<span class="hljs-string">'setInterval'</span>] });

  <span class="hljs-keyword">const</span> expectedIterations = <span class="hljs-number">3</span>;
  <span class="hljs-keyword">const</span> interval = <span class="hljs-number">1000</span>;
  <span class="hljs-keyword">const</span> startedAt = <span class="hljs-title class_">Date</span>.<span class="hljs-title function_">now</span>();
  <span class="hljs-keyword">async</span> <span class="hljs-keyword">function</span> <span class="hljs-title function_">run</span>(<span class="hljs-params"></span>) {
    <span class="hljs-keyword">const</span> times = [];
    <span class="hljs-keyword">for</span> <span class="hljs-title function_">await</span> (<span class="hljs-keyword">const</span> time <span class="hljs-keyword">of</span> nodeTimersPromises.<span class="hljs-built_in">setInterval</span>(interval, startedAt)) {
      times.<span class="hljs-title function_">push</span>(time);
      <span class="hljs-keyword">if</span> (times.<span class="hljs-property">length</span> === expectedIterations) <span class="hljs-keyword">break</span>;
    }
    <span class="hljs-keyword">return</span> times;
  }

  <span class="hljs-keyword">const</span> r = <span class="hljs-title function_">run</span>();
  context.<span class="hljs-property">mock</span>.<span class="hljs-property">timers</span>.<span class="hljs-title function_">tick</span>(interval);
  context.<span class="hljs-property">mock</span>.<span class="hljs-property">timers</span>.<span class="hljs-title function_">tick</span>(interval);
  context.<span class="hljs-property">mock</span>.<span class="hljs-property">timers</span>.<span class="hljs-title function_">tick</span>(interval);

  <span class="hljs-keyword">const</span> timeResults = <span class="hljs-keyword">await</span> r;
  assert.<span class="hljs-title function_">strictEqual</span>(timeResults.<span class="hljs-property">length</span>, expectedIterations);
  <span class="hljs-keyword">for</span> (<span class="hljs-keyword">let</span> it = <span class="hljs-number">1</span>; it &#x3C; expectedIterations; it++) {
    assert.<span class="hljs-title function_">strictEqual</span>(timeResults[it - <span class="hljs-number">1</span>], startedAt + (interval * it));
  }
});</code><button class="copy-button">copy</button></pre>
<h4><code>timers.runAll()</code><span><a class="mark" href="#timersrunall" id="timersrunall">#</a></span><a aria-hidden="true" class="legacy" id="test_timers_runall"></a></h4>
<div class="api_metadata">
<span>Added in: v20.4.0, v18.19.0</span>
</div>
<p>Triggers all pending mocked timers immediately. If the <code>Date</code> object is also
mocked, it will also advance the <code>Date</code> object to the furthest timer's time.</p>
<p>The example below triggers all pending timers immediately,
causing them to execute without any delay.</p>

<pre class="with-38-chars"><input class="js-flavor-toggle" type="checkbox" checked aria-label="Show modern ES modules syntax"><code class="language-js mjs"><span class="hljs-keyword">import</span> assert <span class="hljs-keyword">from</span> <span class="hljs-string">'node:assert'</span>;
<span class="hljs-keyword">import</span> { test } <span class="hljs-keyword">from</span> <span class="hljs-string">'node:test'</span>;

<span class="hljs-title function_">test</span>(<span class="hljs-string">'runAll functions following the given order'</span>, <span class="hljs-function">(<span class="hljs-params">context</span>) =></span> {
  context.<span class="hljs-property">mock</span>.<span class="hljs-property">timers</span>.<span class="hljs-title function_">enable</span>({ <span class="hljs-attr">apis</span>: [<span class="hljs-string">'setTimeout'</span>, <span class="hljs-string">'Date'</span>] });
  <span class="hljs-keyword">const</span> results = [];
  <span class="hljs-built_in">setTimeout</span>(<span class="hljs-function">() =></span> results.<span class="hljs-title function_">push</span>(<span class="hljs-number">1</span>), <span class="hljs-number">9999</span>);

  <span class="hljs-comment">// Notice that if both timers have the same timeout,</span>
  <span class="hljs-comment">// the order of execution is guaranteed</span>
  <span class="hljs-built_in">setTimeout</span>(<span class="hljs-function">() =></span> results.<span class="hljs-title function_">push</span>(<span class="hljs-number">3</span>), <span class="hljs-number">8888</span>);
  <span class="hljs-built_in">setTimeout</span>(<span class="hljs-function">() =></span> results.<span class="hljs-title function_">push</span>(<span class="hljs-number">2</span>), <span class="hljs-number">8888</span>);

  assert.<span class="hljs-title function_">deepStrictEqual</span>(results, []);

  context.<span class="hljs-property">mock</span>.<span class="hljs-property">timers</span>.<span class="hljs-title function_">runAll</span>();
  assert.<span class="hljs-title function_">deepStrictEqual</span>(results, [<span class="hljs-number">3</span>, <span class="hljs-number">2</span>, <span class="hljs-number">1</span>]);
  <span class="hljs-comment">// The Date object is also advanced to the furthest timer's time</span>
  assert.<span class="hljs-title function_">strictEqual</span>(<span class="hljs-title class_">Date</span>.<span class="hljs-title function_">now</span>(), <span class="hljs-number">9999</span>);
});</code><code class="language-js cjs"><span class="hljs-keyword">const</span> assert = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:assert'</span>);
<span class="hljs-keyword">const</span> { test } = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:test'</span>);

<span class="hljs-title function_">test</span>(<span class="hljs-string">'runAll functions following the given order'</span>, <span class="hljs-function">(<span class="hljs-params">context</span>) =></span> {
  context.<span class="hljs-property">mock</span>.<span class="hljs-property">timers</span>.<span class="hljs-title function_">enable</span>({ <span class="hljs-attr">apis</span>: [<span class="hljs-string">'setTimeout'</span>, <span class="hljs-string">'Date'</span>] });
  <span class="hljs-keyword">const</span> results = [];
  <span class="hljs-built_in">setTimeout</span>(<span class="hljs-function">() =></span> results.<span class="hljs-title function_">push</span>(<span class="hljs-number">1</span>), <span class="hljs-number">9999</span>);

  <span class="hljs-comment">// Notice that if both timers have the same timeout,</span>
  <span class="hljs-comment">// the order of execution is guaranteed</span>
  <span class="hljs-built_in">setTimeout</span>(<span class="hljs-function">() =></span> results.<span class="hljs-title function_">push</span>(<span class="hljs-number">3</span>), <span class="hljs-number">8888</span>);
  <span class="hljs-built_in">setTimeout</span>(<span class="hljs-function">() =></span> results.<span class="hljs-title function_">push</span>(<span class="hljs-number">2</span>), <span class="hljs-number">8888</span>);

  assert.<span class="hljs-title function_">deepStrictEqual</span>(results, []);

  context.<span class="hljs-property">mock</span>.<span class="hljs-property">timers</span>.<span class="hljs-title function_">runAll</span>();
  assert.<span class="hljs-title function_">deepStrictEqual</span>(results, [<span class="hljs-number">3</span>, <span class="hljs-number">2</span>, <span class="hljs-number">1</span>]);
  <span class="hljs-comment">// The Date object is also advanced to the furthest timer's time</span>
  assert.<span class="hljs-title function_">strictEqual</span>(<span class="hljs-title class_">Date</span>.<span class="hljs-title function_">now</span>(), <span class="hljs-number">9999</span>);
});</code><button class="copy-button">copy</button></pre>
<p><strong>Note:</strong> The <code>runAll()</code> function is specifically designed for
triggering timers in the context of timer mocking.
It does not have any effect on real-time system
clocks or actual timers outside of the mocking environment.</p>
<h4><code>timers.setTime(milliseconds)</code><span><a class="mark" href="#timerssettimemilliseconds" id="timerssettimemilliseconds">#</a></span><a aria-hidden="true" class="legacy" id="test_timers_settime_milliseconds"></a></h4>
<div class="api_metadata">
<span>Added in: v21.2.0, v20.11.0</span>
</div>
<p>Sets the current Unix timestamp that will be used as reference for any mocked
<code>Date</code> objects.</p>

<pre class="with-38-chars"><input class="js-flavor-toggle" type="checkbox" checked aria-label="Show modern ES modules syntax"><code class="language-js mjs"><span class="hljs-keyword">import</span> assert <span class="hljs-keyword">from</span> <span class="hljs-string">'node:assert'</span>;
<span class="hljs-keyword">import</span> { test } <span class="hljs-keyword">from</span> <span class="hljs-string">'node:test'</span>;

<span class="hljs-title function_">test</span>(<span class="hljs-string">'runAll functions following the given order'</span>, <span class="hljs-function">(<span class="hljs-params">context</span>) =></span> {
  <span class="hljs-keyword">const</span> now = <span class="hljs-title class_">Date</span>.<span class="hljs-title function_">now</span>();
  <span class="hljs-keyword">const</span> setTime = <span class="hljs-number">1000</span>;
  <span class="hljs-comment">// Date.now is not mocked</span>
  assert.<span class="hljs-title function_">deepStrictEqual</span>(<span class="hljs-title class_">Date</span>.<span class="hljs-title function_">now</span>(), now);

  context.<span class="hljs-property">mock</span>.<span class="hljs-property">timers</span>.<span class="hljs-title function_">enable</span>({ <span class="hljs-attr">apis</span>: [<span class="hljs-string">'Date'</span>] });
  context.<span class="hljs-property">mock</span>.<span class="hljs-property">timers</span>.<span class="hljs-title function_">setTime</span>(setTime);
  <span class="hljs-comment">// Date.now is now 1000</span>
  assert.<span class="hljs-title function_">strictEqual</span>(<span class="hljs-title class_">Date</span>.<span class="hljs-title function_">now</span>(), setTime);
});</code><code class="language-js cjs"><span class="hljs-keyword">const</span> assert = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:assert'</span>);
<span class="hljs-keyword">const</span> { test } = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:test'</span>);

<span class="hljs-title function_">test</span>(<span class="hljs-string">'setTime replaces current time'</span>, <span class="hljs-function">(<span class="hljs-params">context</span>) =></span> {
  <span class="hljs-keyword">const</span> now = <span class="hljs-title class_">Date</span>.<span class="hljs-title function_">now</span>();
  <span class="hljs-keyword">const</span> setTime = <span class="hljs-number">1000</span>;
  <span class="hljs-comment">// Date.now is not mocked</span>
  assert.<span class="hljs-title function_">deepStrictEqual</span>(<span class="hljs-title class_">Date</span>.<span class="hljs-title function_">now</span>(), now);

  context.<span class="hljs-property">mock</span>.<span class="hljs-property">timers</span>.<span class="hljs-title function_">enable</span>({ <span class="hljs-attr">apis</span>: [<span class="hljs-string">'Date'</span>] });
  context.<span class="hljs-property">mock</span>.<span class="hljs-property">timers</span>.<span class="hljs-title function_">setTime</span>(setTime);
  <span class="hljs-comment">// Date.now is now 1000</span>
  assert.<span class="hljs-title function_">strictEqual</span>(<span class="hljs-title class_">Date</span>.<span class="hljs-title function_">now</span>(), setTime);
});</code><button class="copy-button">copy</button></pre>
<h5>Dates and Timers working together<span><a class="mark" href="#dates-and-timers-working-together" id="dates-and-timers-working-together">#</a></span><a aria-hidden="true" class="legacy" id="test_dates_and_timers_working_together"></a></h5>
<p>Dates and timer objects are dependent on each other. If you use <code>setTime()</code> to
pass the current time to the mocked <code>Date</code> object, the set timers with
<code>setTimeout</code> and <code>setInterval</code> will <strong>not</strong> be affected.</p>
<p>However, the <code>tick</code> method <strong>will</strong> advanced the mocked <code>Date</code> object.</p>

<pre class="with-38-chars"><input class="js-flavor-toggle" type="checkbox" checked aria-label="Show modern ES modules syntax"><code class="language-js mjs"><span class="hljs-keyword">import</span> assert <span class="hljs-keyword">from</span> <span class="hljs-string">'node:assert'</span>;
<span class="hljs-keyword">import</span> { test } <span class="hljs-keyword">from</span> <span class="hljs-string">'node:test'</span>;

<span class="hljs-title function_">test</span>(<span class="hljs-string">'runAll functions following the given order'</span>, <span class="hljs-function">(<span class="hljs-params">context</span>) =></span> {
  context.<span class="hljs-property">mock</span>.<span class="hljs-property">timers</span>.<span class="hljs-title function_">enable</span>({ <span class="hljs-attr">apis</span>: [<span class="hljs-string">'setTimeout'</span>, <span class="hljs-string">'Date'</span>] });
  <span class="hljs-keyword">const</span> results = [];
  <span class="hljs-built_in">setTimeout</span>(<span class="hljs-function">() =></span> results.<span class="hljs-title function_">push</span>(<span class="hljs-number">1</span>), <span class="hljs-number">9999</span>);

  assert.<span class="hljs-title function_">deepStrictEqual</span>(results, []);
  context.<span class="hljs-property">mock</span>.<span class="hljs-property">timers</span>.<span class="hljs-title function_">setTime</span>(<span class="hljs-number">12000</span>);
  assert.<span class="hljs-title function_">deepStrictEqual</span>(results, []);
  <span class="hljs-comment">// The date is advanced but the timers don't tick</span>
  assert.<span class="hljs-title function_">strictEqual</span>(<span class="hljs-title class_">Date</span>.<span class="hljs-title function_">now</span>(), <span class="hljs-number">12000</span>);
});</code><code class="language-js cjs"><span class="hljs-keyword">const</span> assert = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:assert'</span>);
<span class="hljs-keyword">const</span> { test } = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:test'</span>);

<span class="hljs-title function_">test</span>(<span class="hljs-string">'runAll functions following the given order'</span>, <span class="hljs-function">(<span class="hljs-params">context</span>) =></span> {
  context.<span class="hljs-property">mock</span>.<span class="hljs-property">timers</span>.<span class="hljs-title function_">enable</span>({ <span class="hljs-attr">apis</span>: [<span class="hljs-string">'setTimeout'</span>, <span class="hljs-string">'Date'</span>] });
  <span class="hljs-keyword">const</span> results = [];
  <span class="hljs-built_in">setTimeout</span>(<span class="hljs-function">() =></span> results.<span class="hljs-title function_">push</span>(<span class="hljs-number">1</span>), <span class="hljs-number">9999</span>);

  assert.<span class="hljs-title function_">deepStrictEqual</span>(results, []);
  context.<span class="hljs-property">mock</span>.<span class="hljs-property">timers</span>.<span class="hljs-title function_">setTime</span>(<span class="hljs-number">12000</span>);
  assert.<span class="hljs-title function_">deepStrictEqual</span>(results, []);
  <span class="hljs-comment">// The date is advanced but the timers don't tick</span>
  assert.<span class="hljs-title function_">strictEqual</span>(<span class="hljs-title class_">Date</span>.<span class="hljs-title function_">now</span>(), <span class="hljs-number">12000</span>);
});</code><button class="copy-button">copy</button></pre>
</section><section><h3>Class: <code>TestsStream</code><span><a class="mark" href="#class-testsstream" id="class-testsstream">#</a></span><a aria-hidden="true" class="legacy" id="test_class_testsstream"></a></h3>
<div class="api_metadata">
<details class="changelog"><summary>History</summary>
<table>
<tbody><tr><th>Version</th><th>Changes</th></tr>
<tr><td>v20.0.0, v19.9.0, v18.17.0</td>
<td><p>added type to test:pass and test:fail events for when the test is a suite.</p></td></tr>
<tr><td>v18.9.0, v16.19.0</td>
<td><p><span>Added in: v18.9.0, v16.19.0</span></p></td></tr>
</tbody></table>
</details>
</div>
<ul>
<li>Extends <a href="stream.html#class-streamreadable" class="type">&#x3C;Readable></a></li>
</ul>
<p>A successful call to <a href="#runoptions"><code>run()</code></a> method will return a new <a href="test.html#class-testsstream" class="type">&#x3C;TestsStream></a>
object, streaming a series of events representing the execution of the tests.
<code>TestsStream</code> will emit events, in the order of the tests definition</p>
<p>Some of the events are guaranteed to be emitted in the same order as the tests
are defined, while others are emitted in the order that the tests execute.</p>
<h4>Event: <code>'test:coverage'</code><span><a class="mark" href="#event-testcoverage" id="event-testcoverage">#</a></span><a aria-hidden="true" class="legacy" id="test_event_test_coverage"></a></h4>
<ul>
<li><code>data</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type">&#x3C;Object></a>
<ul>
<li><code>summary</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type">&#x3C;Object></a> An object containing the coverage report.
<ul>
<li><code>files</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array" class="type">&#x3C;Array></a> An array of coverage reports for individual files. Each
report is an object with the following schema:
<ul>
<li><code>path</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type">&#x3C;string></a> The absolute path of the file.</li>
<li><code>totalLineCount</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type">&#x3C;number></a> The total number of lines.</li>
<li><code>totalBranchCount</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type">&#x3C;number></a> The total number of branches.</li>
<li><code>totalFunctionCount</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type">&#x3C;number></a> The total number of functions.</li>
<li><code>coveredLineCount</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type">&#x3C;number></a> The number of covered lines.</li>
<li><code>coveredBranchCount</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type">&#x3C;number></a> The number of covered branches.</li>
<li><code>coveredFunctionCount</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type">&#x3C;number></a> The number of covered functions.</li>
<li><code>coveredLinePercent</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type">&#x3C;number></a> The percentage of lines covered.</li>
<li><code>coveredBranchPercent</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type">&#x3C;number></a> The percentage of branches covered.</li>
<li><code>coveredFunctionPercent</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type">&#x3C;number></a> The percentage of functions covered.</li>
<li><code>functions</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array" class="type">&#x3C;Array></a> An array of functions representing function
coverage.
<ul>
<li><code>name</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type">&#x3C;string></a> The name of the function.</li>
<li><code>line</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type">&#x3C;number></a> The line number where the function is defined.</li>
<li><code>count</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type">&#x3C;number></a> The number of times the function was called.</li>
</ul>
</li>
<li><code>branches</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array" class="type">&#x3C;Array></a> An array of branches representing branch coverage.
<ul>
<li><code>line</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type">&#x3C;number></a> The line number where the branch is defined.</li>
<li><code>count</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type">&#x3C;number></a> The number of times the branch was taken.</li>
</ul>
</li>
<li><code>lines</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array" class="type">&#x3C;Array></a> An array of lines representing line
numbers and the number of times they were covered.
<ul>
<li><code>line</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type">&#x3C;number></a> The line number.</li>
<li><code>count</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type">&#x3C;number></a> The number of times the line was covered.</li>
</ul>
</li>
</ul>
</li>
<li><code>thresholds</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type">&#x3C;Object></a> An object containing whether or not the coverage for
each coverage type.
<ul>
<li><code>function</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type">&#x3C;number></a> The function coverage threshold.</li>
<li><code>branch</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type">&#x3C;number></a> The branch coverage threshold.</li>
<li><code>line</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type">&#x3C;number></a> The line coverage threshold.</li>
</ul>
</li>
<li><code>totals</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type">&#x3C;Object></a> An object containing a summary of coverage for all
files.
<ul>
<li><code>totalLineCount</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type">&#x3C;number></a> The total number of lines.</li>
<li><code>totalBranchCount</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type">&#x3C;number></a> The total number of branches.</li>
<li><code>totalFunctionCount</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type">&#x3C;number></a> The total number of functions.</li>
<li><code>coveredLineCount</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type">&#x3C;number></a> The number of covered lines.</li>
<li><code>coveredBranchCount</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type">&#x3C;number></a> The number of covered branches.</li>
<li><code>coveredFunctionCount</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type">&#x3C;number></a> The number of covered functions.</li>
<li><code>coveredLinePercent</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type">&#x3C;number></a> The percentage of lines covered.</li>
<li><code>coveredBranchPercent</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type">&#x3C;number></a> The percentage of branches covered.</li>
<li><code>coveredFunctionPercent</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type">&#x3C;number></a> The percentage of functions covered.</li>
</ul>
</li>
<li><code>workingDirectory</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type">&#x3C;string></a> The working directory when code coverage
began. This is useful for displaying relative path names in case the tests
changed the working directory of the Node.js process.</li>
</ul>
</li>
<li><code>nesting</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type">&#x3C;number></a> The nesting level of the test.</li>
</ul>
</li>
</ul>
<p>Emitted when code coverage is enabled and all tests have completed.</p>
<h4>Event: <code>'test:complete'</code><span><a class="mark" href="#event-testcomplete" id="event-testcomplete">#</a></span><a aria-hidden="true" class="legacy" id="test_event_test_complete"></a></h4>
<ul>
<li><code>data</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type">&#x3C;Object></a>
<ul>
<li><code>column</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type">&#x3C;number></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Undefined_type" class="type">&#x3C;undefined></a> The column number where the test is defined, or
<code>undefined</code> if the test was run through the REPL.</li>
<li><code>details</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type">&#x3C;Object></a> Additional execution metadata.
<ul>
<li><code>passed</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type">&#x3C;boolean></a> Whether the test passed or not.</li>
<li><code>duration_ms</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type">&#x3C;number></a> The duration of the test in milliseconds.</li>
<li><code>error</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error" class="type">&#x3C;Error></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Undefined_type" class="type">&#x3C;undefined></a> An error wrapping the error thrown by the test
if it did not pass.
<ul>
<li><code>cause</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error" class="type">&#x3C;Error></a> The actual error thrown by the test.</li>
</ul>
</li>
<li><code>type</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type">&#x3C;string></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Undefined_type" class="type">&#x3C;undefined></a> The type of the test, used to denote whether
this is a suite.</li>
</ul>
</li>
<li><code>file</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type">&#x3C;string></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Undefined_type" class="type">&#x3C;undefined></a> The path of the test file,
<code>undefined</code> if test was run through the REPL.</li>
<li><code>line</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type">&#x3C;number></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Undefined_type" class="type">&#x3C;undefined></a> The line number where the test is defined, or
<code>undefined</code> if the test was run through the REPL.</li>
<li><code>name</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type">&#x3C;string></a> The test name.</li>
<li><code>nesting</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type">&#x3C;number></a> The nesting level of the test.</li>
<li><code>testNumber</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type">&#x3C;number></a> The ordinal number of the test.</li>
<li><code>todo</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type">&#x3C;string></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type">&#x3C;boolean></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Undefined_type" class="type">&#x3C;undefined></a> Present if <a href="#contexttodomessage"><code>context.todo</code></a> is called</li>
<li><code>skip</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type">&#x3C;string></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type">&#x3C;boolean></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Undefined_type" class="type">&#x3C;undefined></a> Present if <a href="#contextskipmessage"><code>context.skip</code></a> is called</li>
</ul>
</li>
</ul>
<p>Emitted when a test completes its execution.
This event is not emitted in the same order as the tests are
defined.
The corresponding declaration ordered events are <code>'test:pass'</code> and <code>'test:fail'</code>.</p>
<h4>Event: <code>'test:dequeue'</code><span><a class="mark" href="#event-testdequeue" id="event-testdequeue">#</a></span><a aria-hidden="true" class="legacy" id="test_event_test_dequeue"></a></h4>
<ul>
<li><code>data</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type">&#x3C;Object></a>
<ul>
<li><code>column</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type">&#x3C;number></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Undefined_type" class="type">&#x3C;undefined></a> The column number where the test is defined, or
<code>undefined</code> if the test was run through the REPL.</li>
<li><code>file</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type">&#x3C;string></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Undefined_type" class="type">&#x3C;undefined></a> The path of the test file,
<code>undefined</code> if test was run through the REPL.</li>
<li><code>line</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type">&#x3C;number></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Undefined_type" class="type">&#x3C;undefined></a> The line number where the test is defined, or
<code>undefined</code> if the test was run through the REPL.</li>
<li><code>name</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type">&#x3C;string></a> The test name.</li>
<li><code>nesting</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type">&#x3C;number></a> The nesting level of the test.</li>
</ul>
</li>
</ul>
<p>Emitted when a test is dequeued, right before it is executed.
This event is not guaranteed to be emitted in the same order as the tests are
defined. The corresponding declaration ordered event is <code>'test:start'</code>.</p>
<h4>Event: <code>'test:diagnostic'</code><span><a class="mark" href="#event-testdiagnostic" id="event-testdiagnostic">#</a></span><a aria-hidden="true" class="legacy" id="test_event_test_diagnostic"></a></h4>
<ul>
<li><code>data</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type">&#x3C;Object></a>
<ul>
<li><code>column</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type">&#x3C;number></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Undefined_type" class="type">&#x3C;undefined></a> The column number where the test is defined, or
<code>undefined</code> if the test was run through the REPL.</li>
<li><code>file</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type">&#x3C;string></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Undefined_type" class="type">&#x3C;undefined></a> The path of the test file,
<code>undefined</code> if test was run through the REPL.</li>
<li><code>line</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type">&#x3C;number></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Undefined_type" class="type">&#x3C;undefined></a> The line number where the test is defined, or
<code>undefined</code> if the test was run through the REPL.</li>
<li><code>message</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type">&#x3C;string></a> The diagnostic message.</li>
<li><code>nesting</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type">&#x3C;number></a> The nesting level of the test.</li>
</ul>
</li>
</ul>
<p>Emitted when <a href="#contextdiagnosticmessage"><code>context.diagnostic</code></a> is called.
This event is guaranteed to be emitted in the same order as the tests are
defined.</p>
<h4>Event: <code>'test:enqueue'</code><span><a class="mark" href="#event-testenqueue" id="event-testenqueue">#</a></span><a aria-hidden="true" class="legacy" id="test_event_test_enqueue"></a></h4>
<ul>
<li><code>data</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type">&#x3C;Object></a>
<ul>
<li><code>column</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type">&#x3C;number></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Undefined_type" class="type">&#x3C;undefined></a> The column number where the test is defined, or
<code>undefined</code> if the test was run through the REPL.</li>
<li><code>file</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type">&#x3C;string></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Undefined_type" class="type">&#x3C;undefined></a> The path of the test file,
<code>undefined</code> if test was run through the REPL.</li>
<li><code>line</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type">&#x3C;number></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Undefined_type" class="type">&#x3C;undefined></a> The line number where the test is defined, or
<code>undefined</code> if the test was run through the REPL.</li>
<li><code>name</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type">&#x3C;string></a> The test name.</li>
<li><code>nesting</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type">&#x3C;number></a> The nesting level of the test.</li>
</ul>
</li>
</ul>
<p>Emitted when a test is enqueued for execution.</p>
<h4>Event: <code>'test:fail'</code><span><a class="mark" href="#event-testfail" id="event-testfail">#</a></span><a aria-hidden="true" class="legacy" id="test_event_test_fail"></a></h4>
<ul>
<li><code>data</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type">&#x3C;Object></a>
<ul>
<li><code>column</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type">&#x3C;number></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Undefined_type" class="type">&#x3C;undefined></a> The column number where the test is defined, or
<code>undefined</code> if the test was run through the REPL.</li>
<li><code>details</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type">&#x3C;Object></a> Additional execution metadata.
<ul>
<li><code>duration_ms</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type">&#x3C;number></a> The duration of the test in milliseconds.</li>
<li><code>error</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error" class="type">&#x3C;Error></a> An error wrapping the error thrown by the test.
<ul>
<li><code>cause</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error" class="type">&#x3C;Error></a> The actual error thrown by the test.</li>
</ul>
</li>
<li><code>type</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type">&#x3C;string></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Undefined_type" class="type">&#x3C;undefined></a> The type of the test, used to denote whether
this is a suite.</li>
</ul>
</li>
<li><code>file</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type">&#x3C;string></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Undefined_type" class="type">&#x3C;undefined></a> The path of the test file,
<code>undefined</code> if test was run through the REPL.</li>
<li><code>line</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type">&#x3C;number></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Undefined_type" class="type">&#x3C;undefined></a> The line number where the test is defined, or
<code>undefined</code> if the test was run through the REPL.</li>
<li><code>name</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type">&#x3C;string></a> The test name.</li>
<li><code>nesting</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type">&#x3C;number></a> The nesting level of the test.</li>
<li><code>testNumber</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type">&#x3C;number></a> The ordinal number of the test.</li>
<li><code>todo</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type">&#x3C;string></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type">&#x3C;boolean></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Undefined_type" class="type">&#x3C;undefined></a> Present if <a href="#contexttodomessage"><code>context.todo</code></a> is called</li>
<li><code>skip</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type">&#x3C;string></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type">&#x3C;boolean></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Undefined_type" class="type">&#x3C;undefined></a> Present if <a href="#contextskipmessage"><code>context.skip</code></a> is called</li>
</ul>
</li>
</ul>
<p>Emitted when a test fails.
This event is guaranteed to be emitted in the same order as the tests are
defined.
The corresponding execution ordered event is <code>'test:complete'</code>.</p>
<h4>Event: <code>'test:pass'</code><span><a class="mark" href="#event-testpass" id="event-testpass">#</a></span><a aria-hidden="true" class="legacy" id="test_event_test_pass"></a></h4>
<ul>
<li><code>data</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type">&#x3C;Object></a>
<ul>
<li><code>column</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type">&#x3C;number></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Undefined_type" class="type">&#x3C;undefined></a> The column number where the test is defined, or
<code>undefined</code> if the test was run through the REPL.</li>
<li><code>details</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type">&#x3C;Object></a> Additional execution metadata.
<ul>
<li><code>duration_ms</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type">&#x3C;number></a> The duration of the test in milliseconds.</li>
<li><code>type</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type">&#x3C;string></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Undefined_type" class="type">&#x3C;undefined></a> The type of the test, used to denote whether
this is a suite.</li>
</ul>
</li>
<li><code>file</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type">&#x3C;string></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Undefined_type" class="type">&#x3C;undefined></a> The path of the test file,
<code>undefined</code> if test was run through the REPL.</li>
<li><code>line</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type">&#x3C;number></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Undefined_type" class="type">&#x3C;undefined></a> The line number where the test is defined, or
<code>undefined</code> if the test was run through the REPL.</li>
<li><code>name</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type">&#x3C;string></a> The test name.</li>
<li><code>nesting</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type">&#x3C;number></a> The nesting level of the test.</li>
<li><code>testNumber</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type">&#x3C;number></a> The ordinal number of the test.</li>
<li><code>todo</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type">&#x3C;string></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type">&#x3C;boolean></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Undefined_type" class="type">&#x3C;undefined></a> Present if <a href="#contexttodomessage"><code>context.todo</code></a> is called</li>
<li><code>skip</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type">&#x3C;string></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type">&#x3C;boolean></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Undefined_type" class="type">&#x3C;undefined></a> Present if <a href="#contextskipmessage"><code>context.skip</code></a> is called</li>
</ul>
</li>
</ul>
<p>Emitted when a test passes.
This event is guaranteed to be emitted in the same order as the tests are
defined.
The corresponding execution ordered event is <code>'test:complete'</code>.</p>
<h4>Event: <code>'test:plan'</code><span><a class="mark" href="#event-testplan" id="event-testplan">#</a></span><a aria-hidden="true" class="legacy" id="test_event_test_plan"></a></h4>
<ul>
<li><code>data</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type">&#x3C;Object></a>
<ul>
<li><code>column</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type">&#x3C;number></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Undefined_type" class="type">&#x3C;undefined></a> The column number where the test is defined, or
<code>undefined</code> if the test was run through the REPL.</li>
<li><code>file</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type">&#x3C;string></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Undefined_type" class="type">&#x3C;undefined></a> The path of the test file,
<code>undefined</code> if test was run through the REPL.</li>
<li><code>line</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type">&#x3C;number></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Undefined_type" class="type">&#x3C;undefined></a> The line number where the test is defined, or
<code>undefined</code> if the test was run through the REPL.</li>
<li><code>nesting</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type">&#x3C;number></a> The nesting level of the test.</li>
<li><code>count</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type">&#x3C;number></a> The number of subtests that have ran.</li>
</ul>
</li>
</ul>
<p>Emitted when all subtests have completed for a given test.
This event is guaranteed to be emitted in the same order as the tests are
defined.</p>
<h4>Event: <code>'test:start'</code><span><a class="mark" href="#event-teststart" id="event-teststart">#</a></span><a aria-hidden="true" class="legacy" id="test_event_test_start"></a></h4>
<ul>
<li><code>data</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type">&#x3C;Object></a>
<ul>
<li><code>column</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type">&#x3C;number></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Undefined_type" class="type">&#x3C;undefined></a> The column number where the test is defined, or
<code>undefined</code> if the test was run through the REPL.</li>
<li><code>file</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type">&#x3C;string></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Undefined_type" class="type">&#x3C;undefined></a> The path of the test file,
<code>undefined</code> if test was run through the REPL.</li>
<li><code>line</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type">&#x3C;number></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Undefined_type" class="type">&#x3C;undefined></a> The line number where the test is defined, or
<code>undefined</code> if the test was run through the REPL.</li>
<li><code>name</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type">&#x3C;string></a> The test name.</li>
<li><code>nesting</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type">&#x3C;number></a> The nesting level of the test.</li>
</ul>
</li>
</ul>
<p>Emitted when a test starts reporting its own and its subtests status.
This event is guaranteed to be emitted in the same order as the tests are
defined.
The corresponding execution ordered event is <code>'test:dequeue'</code>.</p>
<h4>Event: <code>'test:stderr'</code><span><a class="mark" href="#event-teststderr" id="event-teststderr">#</a></span><a aria-hidden="true" class="legacy" id="test_event_test_stderr"></a></h4>
<ul>
<li><code>data</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type">&#x3C;Object></a>
<ul>
<li><code>file</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type">&#x3C;string></a> The path of the test file.</li>
<li><code>message</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type">&#x3C;string></a> The message written to <code>stderr</code>.</li>
</ul>
</li>
</ul>
<p>Emitted when a running test writes to <code>stderr</code>.
This event is only emitted if <code>--test</code> flag is passed.
This event is not guaranteed to be emitted in the same order as the tests are
defined.</p>
<h4>Event: <code>'test:stdout'</code><span><a class="mark" href="#event-teststdout" id="event-teststdout">#</a></span><a aria-hidden="true" class="legacy" id="test_event_test_stdout"></a></h4>
<ul>
<li><code>data</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type">&#x3C;Object></a>
<ul>
<li><code>file</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type">&#x3C;string></a> The path of the test file.</li>
<li><code>message</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type">&#x3C;string></a> The message written to <code>stdout</code>.</li>
</ul>
</li>
</ul>
<p>Emitted when a running test writes to <code>stdout</code>.
This event is only emitted if <code>--test</code> flag is passed.
This event is not guaranteed to be emitted in the same order as the tests are
defined.</p>
<h4>Event: <code>'test:summary'</code><span><a class="mark" href="#event-testsummary" id="event-testsummary">#</a></span><a aria-hidden="true" class="legacy" id="test_event_test_summary"></a></h4>
<ul>
<li><code>data</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type">&#x3C;Object></a>
<ul>
<li><code>counts</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type">&#x3C;Object></a> An object containing the counts of various test results.
<ul>
<li><code>cancelled</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type">&#x3C;number></a> The total number of cancelled tests.</li>
<li><code>failed</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type">&#x3C;number></a> The total number of failed tests.</li>
<li><code>passed</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type">&#x3C;number></a> The total number of passed tests.</li>
<li><code>skipped</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type">&#x3C;number></a> The total number of skipped tests.</li>
<li><code>suites</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type">&#x3C;number></a> The total number of suites run.</li>
<li><code>tests</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type">&#x3C;number></a> The total number of tests run, excluding suites.</li>
<li><code>todo</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type">&#x3C;number></a> The total number of TODO tests.</li>
<li><code>topLevel</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type">&#x3C;number></a> The total number of top level tests and suites.</li>
</ul>
</li>
<li><code>duration_ms</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type">&#x3C;number></a> The duration of the test run in milliseconds.</li>
<li><code>file</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type">&#x3C;string></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Undefined_type" class="type">&#x3C;undefined></a> The path of the test file that generated the
summary. If the summary corresponds to multiple files, this value is
<code>undefined</code>.</li>
<li><code>success</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type">&#x3C;boolean></a> Indicates whether or not the test run is considered
successful or not. If any error condition occurs, such as a failing test or
unmet coverage threshold, this value will be set to <code>false</code>.</li>
</ul>
</li>
</ul>
<p>Emitted when a test run completes. This event contains metrics pertaining to
the completed test run, and is useful for determining if a test run passed or
failed. If process-level test isolation is used, a <code>'test:summary'</code> event is
generated for each test file in addition to a final cumulative summary.</p>
<h4>Event: <code>'test:watch:drained'</code><span><a class="mark" href="#event-testwatchdrained" id="event-testwatchdrained">#</a></span><a aria-hidden="true" class="legacy" id="test_event_test_watch_drained"></a></h4>
<p>Emitted when no more tests are queued for execution in watch mode.</p>
</section><section><h3>Class: <code>TestContext</code><span><a class="mark" href="#class-testcontext" id="class-testcontext">#</a></span><a aria-hidden="true" class="legacy" id="test_class_testcontext"></a></h3>
<div class="api_metadata">
<details class="changelog"><summary>History</summary>
<table>
<tbody><tr><th>Version</th><th>Changes</th></tr>
<tr><td>v20.1.0, v18.17.0</td>
<td><p>The <code>before</code> function was added to TestContext.</p></td></tr>
<tr><td>v18.0.0, v16.17.0</td>
<td><p><span>Added in: v18.0.0, v16.17.0</span></p></td></tr>
</tbody></table>
</details>
</div>
<p>An instance of <code>TestContext</code> is passed to each test function in order to
interact with the test runner. However, the <code>TestContext</code> constructor is not
exposed as part of the API.</p>
<h4><code>context.before([fn][, options])</code><span><a class="mark" href="#contextbeforefn-options" id="contextbeforefn-options">#</a></span><a aria-hidden="true" class="legacy" id="test_context_before_fn_options"></a></h4>
<div class="api_metadata">
<span>Added in: v20.1.0, v18.17.0</span>
</div>
<ul>
<li><code>fn</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type">&#x3C;Function></a> | <a href="https://tc39.es/ecma262/#sec-async-function-constructor" class="type">&#x3C;AsyncFunction></a> The hook function. The first argument
to this function is a <a href="#class-testcontext"><code>TestContext</code></a> object. If the hook uses callbacks,
the callback function is passed as the second argument. <strong>Default:</strong> A no-op
function.</li>
<li><code>options</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type">&#x3C;Object></a> Configuration options for the hook. The following
properties are supported:
<ul>
<li><code>signal</code> <a href="globals.html#class-abortsignal" class="type">&#x3C;AbortSignal></a> Allows aborting an in-progress hook.</li>
<li><code>timeout</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type">&#x3C;number></a> A number of milliseconds the hook will fail after.
If unspecified, subtests inherit this value from their parent.
<strong>Default:</strong> <code>Infinity</code>.</li>
</ul>
</li>
</ul>
<p>This function is used to create a hook running before
subtest of the current test.</p>
<h4><code>context.beforeEach([fn][, options])</code><span><a class="mark" href="#contextbeforeeachfn-options" id="contextbeforeeachfn-options">#</a></span><a aria-hidden="true" class="legacy" id="test_context_beforeeach_fn_options"></a></h4>
<div class="api_metadata">
<span>Added in: v18.8.0, v16.18.0</span>
</div>
<ul>
<li><code>fn</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type">&#x3C;Function></a> | <a href="https://tc39.es/ecma262/#sec-async-function-constructor" class="type">&#x3C;AsyncFunction></a> The hook function. The first argument
to this function is a <a href="#class-testcontext"><code>TestContext</code></a> object. If the hook uses callbacks,
the callback function is passed as the second argument. <strong>Default:</strong> A no-op
function.</li>
<li><code>options</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type">&#x3C;Object></a> Configuration options for the hook. The following
properties are supported:
<ul>
<li><code>signal</code> <a href="globals.html#class-abortsignal" class="type">&#x3C;AbortSignal></a> Allows aborting an in-progress hook.</li>
<li><code>timeout</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type">&#x3C;number></a> A number of milliseconds the hook will fail after.
If unspecified, subtests inherit this value from their parent.
<strong>Default:</strong> <code>Infinity</code>.</li>
</ul>
</li>
</ul>
<p>This function is used to create a hook running
before each subtest of the current test.</p>
<pre><code class="language-js"><span class="hljs-title function_">test</span>(<span class="hljs-string">'top level test'</span>, <span class="hljs-title function_">async</span> (t) => {
  t.<span class="hljs-title function_">beforeEach</span>(<span class="hljs-function">(<span class="hljs-params">t</span>) =></span> t.<span class="hljs-title function_">diagnostic</span>(<span class="hljs-string">`about to run <span class="hljs-subst">${t.name}</span>`</span>));
  <span class="hljs-keyword">await</span> t.<span class="hljs-title function_">test</span>(
    <span class="hljs-string">'This is a subtest'</span>,
    <span class="hljs-function">(<span class="hljs-params">t</span>) =></span> {
      assert.<span class="hljs-title function_">ok</span>(<span class="hljs-string">'some relevant assertion here'</span>);
    },
  );
});</code> <button class="copy-button">copy</button></pre>
<h4><code>context.after([fn][, options])</code><span><a class="mark" href="#contextafterfn-options" id="contextafterfn-options">#</a></span><a aria-hidden="true" class="legacy" id="test_context_after_fn_options"></a></h4>
<div class="api_metadata">
<span>Added in: v19.3.0, v18.13.0</span>
</div>
<ul>
<li><code>fn</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type">&#x3C;Function></a> | <a href="https://tc39.es/ecma262/#sec-async-function-constructor" class="type">&#x3C;AsyncFunction></a> The hook function. The first argument
to this function is a <a href="#class-testcontext"><code>TestContext</code></a> object. If the hook uses callbacks,
the callback function is passed as the second argument. <strong>Default:</strong> A no-op
function.</li>
<li><code>options</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type">&#x3C;Object></a> Configuration options for the hook. The following
properties are supported:
<ul>
<li><code>signal</code> <a href="globals.html#class-abortsignal" class="type">&#x3C;AbortSignal></a> Allows aborting an in-progress hook.</li>
<li><code>timeout</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type">&#x3C;number></a> A number of milliseconds the hook will fail after.
If unspecified, subtests inherit this value from their parent.
<strong>Default:</strong> <code>Infinity</code>.</li>
</ul>
</li>
</ul>
<p>This function is used to create a hook that runs after the current test
finishes.</p>
<pre><code class="language-js"><span class="hljs-title function_">test</span>(<span class="hljs-string">'top level test'</span>, <span class="hljs-title function_">async</span> (t) => {
  t.<span class="hljs-title function_">after</span>(<span class="hljs-function">(<span class="hljs-params">t</span>) =></span> t.<span class="hljs-title function_">diagnostic</span>(<span class="hljs-string">`finished running <span class="hljs-subst">${t.name}</span>`</span>));
  assert.<span class="hljs-title function_">ok</span>(<span class="hljs-string">'some relevant assertion here'</span>);
});</code> <button class="copy-button">copy</button></pre>
<h4><code>context.afterEach([fn][, options])</code><span><a class="mark" href="#contextaftereachfn-options" id="contextaftereachfn-options">#</a></span><a aria-hidden="true" class="legacy" id="test_context_aftereach_fn_options"></a></h4>
<div class="api_metadata">
<span>Added in: v18.8.0, v16.18.0</span>
</div>
<ul>
<li><code>fn</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type">&#x3C;Function></a> | <a href="https://tc39.es/ecma262/#sec-async-function-constructor" class="type">&#x3C;AsyncFunction></a> The hook function. The first argument
to this function is a <a href="#class-testcontext"><code>TestContext</code></a> object. If the hook uses callbacks,
the callback function is passed as the second argument. <strong>Default:</strong> A no-op
function.</li>
<li><code>options</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type">&#x3C;Object></a> Configuration options for the hook. The following
properties are supported:
<ul>
<li><code>signal</code> <a href="globals.html#class-abortsignal" class="type">&#x3C;AbortSignal></a> Allows aborting an in-progress hook.</li>
<li><code>timeout</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type">&#x3C;number></a> A number of milliseconds the hook will fail after.
If unspecified, subtests inherit this value from their parent.
<strong>Default:</strong> <code>Infinity</code>.</li>
</ul>
</li>
</ul>
<p>This function is used to create a hook running
after each subtest of the current test.</p>
<pre><code class="language-js"><span class="hljs-title function_">test</span>(<span class="hljs-string">'top level test'</span>, <span class="hljs-title function_">async</span> (t) => {
  t.<span class="hljs-title function_">afterEach</span>(<span class="hljs-function">(<span class="hljs-params">t</span>) =></span> t.<span class="hljs-title function_">diagnostic</span>(<span class="hljs-string">`finished running <span class="hljs-subst">${t.name}</span>`</span>));
  <span class="hljs-keyword">await</span> t.<span class="hljs-title function_">test</span>(
    <span class="hljs-string">'This is a subtest'</span>,
    <span class="hljs-function">(<span class="hljs-params">t</span>) =></span> {
      assert.<span class="hljs-title function_">ok</span>(<span class="hljs-string">'some relevant assertion here'</span>);
    },
  );
});</code> <button class="copy-button">copy</button></pre>
<h4><code>context.assert</code><span><a class="mark" href="#contextassert" id="contextassert">#</a></span><a aria-hidden="true" class="legacy" id="test_context_assert"></a></h4>
<div class="api_metadata">
<span>Added in: v22.2.0</span>
</div>
<p>An object containing assertion methods bound to <code>context</code>. The top-level
functions from the <code>node:assert</code> module are exposed here for the purpose of
creating test plans.</p>
<pre><code class="language-js"><span class="hljs-title function_">test</span>(<span class="hljs-string">'test'</span>, <span class="hljs-function">(<span class="hljs-params">t</span>) =></span> {
  t.<span class="hljs-title function_">plan</span>(<span class="hljs-number">1</span>);
  t.<span class="hljs-property">assert</span>.<span class="hljs-title function_">strictEqual</span>(<span class="hljs-literal">true</span>, <span class="hljs-literal">true</span>);
});</code> <button class="copy-button">copy</button></pre>
<h5><code>context.assert.fileSnapshot(value, path[, options])</code><span><a class="mark" href="#contextassertfilesnapshotvalue-path-options" id="contextassertfilesnapshotvalue-path-options">#</a></span><a aria-hidden="true" class="legacy" id="test_context_assert_filesnapshot_value_path_options"></a></h5>
<div class="api_metadata">
<span>Added in: v22.14.0</span>
</div>
<ul>
<li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type">&#x3C;any></a> A value to serialize to a string. If Node.js was started with
the <a href="cli.html#--test-update-snapshots"><code>--test-update-snapshots</code></a> flag, the serialized value is written to
<code>path</code>. Otherwise, the serialized value is compared to the contents of the
existing snapshot file.</li>
<li><code>path</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type">&#x3C;string></a> The file where the serialized <code>value</code> is written.</li>
<li><code>options</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type">&#x3C;Object></a> Optional configuration options. The following properties
are supported:
<ul>
<li><code>serializers</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array" class="type">&#x3C;Array></a> An array of synchronous functions used to serialize
<code>value</code> into a string. <code>value</code> is passed as the only argument to the first
serializer function. The return value of each serializer is passed as input
to the next serializer. Once all serializers have run, the resulting value
is coerced to a string. <strong>Default:</strong> If no serializers are provided, the
test runner's default serializers are used.</li>
</ul>
</li>
</ul>
<p>This function serializes <code>value</code> and writes it to the file specified by <code>path</code>.</p>
<pre><code class="language-js"><span class="hljs-title function_">test</span>(<span class="hljs-string">'snapshot test with default serialization'</span>, <span class="hljs-function">(<span class="hljs-params">t</span>) =></span> {
  t.<span class="hljs-property">assert</span>.<span class="hljs-title function_">fileSnapshot</span>({ <span class="hljs-attr">value1</span>: <span class="hljs-number">1</span>, <span class="hljs-attr">value2</span>: <span class="hljs-number">2</span> }, <span class="hljs-string">'./snapshots/snapshot.json'</span>);
});</code> <button class="copy-button">copy</button></pre>
<p>This function differs from <code>context.assert.snapshot()</code> in the following ways:</p>
<ul>
<li>The snapshot file path is explicitly provided by the user.</li>
<li>Each snapshot file is limited to a single snapshot value.</li>
<li>No additional escaping is performed by the test runner.</li>
</ul>
<p>These differences allow snapshot files to better support features such as syntax
highlighting.</p>
<h5><code>context.assert.snapshot(value[, options])</code><span><a class="mark" href="#contextassertsnapshotvalue-options" id="contextassertsnapshotvalue-options">#</a></span><a aria-hidden="true" class="legacy" id="test_context_assert_snapshot_value_options"></a></h5>
<div class="api_metadata">
<span>Added in: v22.3.0</span>
</div>
<ul>
<li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type">&#x3C;any></a> A value to serialize to a string. If Node.js was started with
the <a href="cli.html#--test-update-snapshots"><code>--test-update-snapshots</code></a> flag, the serialized value is written to
the snapshot file. Otherwise, the serialized value is compared to the
corresponding value in the existing snapshot file.</li>
<li><code>options</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type">&#x3C;Object></a> Optional configuration options. The following properties
are supported:
<ul>
<li><code>serializers</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array" class="type">&#x3C;Array></a> An array of synchronous functions used to serialize
<code>value</code> into a string. <code>value</code> is passed as the only argument to the first
serializer function. The return value of each serializer is passed as input
to the next serializer. Once all serializers have run, the resulting value
is coerced to a string. <strong>Default:</strong> If no serializers are provided, the
test runner's default serializers are used.</li>
</ul>
</li>
</ul>
<p>This function implements assertions for snapshot testing.</p>
<pre><code class="language-js"><span class="hljs-title function_">test</span>(<span class="hljs-string">'snapshot test with default serialization'</span>, <span class="hljs-function">(<span class="hljs-params">t</span>) =></span> {
  t.<span class="hljs-property">assert</span>.<span class="hljs-title function_">snapshot</span>({ <span class="hljs-attr">value1</span>: <span class="hljs-number">1</span>, <span class="hljs-attr">value2</span>: <span class="hljs-number">2</span> });
});

<span class="hljs-title function_">test</span>(<span class="hljs-string">'snapshot test with custom serialization'</span>, <span class="hljs-function">(<span class="hljs-params">t</span>) =></span> {
  t.<span class="hljs-property">assert</span>.<span class="hljs-title function_">snapshot</span>({ <span class="hljs-attr">value3</span>: <span class="hljs-number">3</span>, <span class="hljs-attr">value4</span>: <span class="hljs-number">4</span> }, {
    <span class="hljs-attr">serializers</span>: [<span class="hljs-function">(<span class="hljs-params">value</span>) =></span> <span class="hljs-title class_">JSON</span>.<span class="hljs-title function_">stringify</span>(value)],
  });
});</code> <button class="copy-button">copy</button></pre>
<h4><code>context.diagnostic(message)</code><span><a class="mark" href="#contextdiagnosticmessage" id="contextdiagnosticmessage">#</a></span><a aria-hidden="true" class="legacy" id="test_context_diagnostic_message"></a></h4>
<div class="api_metadata">
<span>Added in: v18.0.0, v16.17.0</span>
</div>
<ul>
<li><code>message</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type">&#x3C;string></a> Message to be reported.</li>
</ul>
<p>This function is used to write diagnostics to the output. Any diagnostic
information is included at the end of the test's results. This function does
not return a value.</p>
<pre><code class="language-js"><span class="hljs-title function_">test</span>(<span class="hljs-string">'top level test'</span>, <span class="hljs-function">(<span class="hljs-params">t</span>) =></span> {
  t.<span class="hljs-title function_">diagnostic</span>(<span class="hljs-string">'A diagnostic message'</span>);
});</code> <button class="copy-button">copy</button></pre>
<h4><code>context.filePath</code><span><a class="mark" href="#contextfilepath" id="contextfilepath">#</a></span><a aria-hidden="true" class="legacy" id="test_context_filepath"></a></h4>
<div class="api_metadata">
<span>Added in: v22.6.0</span>
</div>
<p>The absolute path of the test file that created the current test. If a test file
imports additional modules that generate tests, the imported tests will return
the path of the root test file.</p>
<h4><code>context.fullName</code><span><a class="mark" href="#contextfullname" id="contextfullname">#</a></span><a aria-hidden="true" class="legacy" id="test_context_fullname"></a></h4>
<div class="api_metadata">
<span>Added in: v22.3.0</span>
</div>
<p>The name of the test and each of its ancestors, separated by <code>></code>.</p>
<h4><code>context.name</code><span><a class="mark" href="#contextname" id="contextname">#</a></span><a aria-hidden="true" class="legacy" id="test_context_name"></a></h4>
<div class="api_metadata">
<span>Added in: v18.8.0, v16.18.0</span>
</div>
<p>The name of the test.</p>
<h4><code>context.plan(count)</code><span><a class="mark" href="#contextplancount" id="contextplancount">#</a></span><a aria-hidden="true" class="legacy" id="test_context_plan_count"></a></h4>
<div class="api_metadata">
<details class="changelog"><summary>History</summary>
<table>
<tbody><tr><th>Version</th><th>Changes</th></tr>
<tr><td>v22.13.0</td>
<td><p>This function is no longer experimental.</p></td></tr>
<tr><td>v22.2.0</td>
<td><p><span>Added in: v22.2.0</span></p></td></tr>
</tbody></table>
</details>
</div>
<ul>
<li><code>count</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type">&#x3C;number></a> The number of assertions and subtests that are expected to run.</li>
</ul>
<p>This function is used to set the number of assertions and subtests that are expected to run
within the test. If the number of assertions and subtests that run does not match the
expected count, the test will fail.</p>
<blockquote>
<p>Note: To make sure assertions are tracked, <code>t.assert</code> must be used instead of <code>assert</code> directly.</p>
</blockquote>
<pre><code class="language-js"><span class="hljs-title function_">test</span>(<span class="hljs-string">'top level test'</span>, <span class="hljs-function">(<span class="hljs-params">t</span>) =></span> {
  t.<span class="hljs-title function_">plan</span>(<span class="hljs-number">2</span>);
  t.<span class="hljs-property">assert</span>.<span class="hljs-title function_">ok</span>(<span class="hljs-string">'some relevant assertion here'</span>);
  t.<span class="hljs-title function_">test</span>(<span class="hljs-string">'subtest'</span>, <span class="hljs-function">() =></span> {});
});</code> <button class="copy-button">copy</button></pre>
<p>When working with asynchronous code, the <code>plan</code> function can be used to ensure that the
correct number of assertions are run:</p>
<pre><code class="language-js"><span class="hljs-title function_">test</span>(<span class="hljs-string">'planning with streams'</span>, <span class="hljs-function">(<span class="hljs-params">t, done</span>) =></span> {
  <span class="hljs-keyword">function</span>* <span class="hljs-title function_">generate</span>(<span class="hljs-params"></span>) {
    <span class="hljs-keyword">yield</span> <span class="hljs-string">'a'</span>;
    <span class="hljs-keyword">yield</span> <span class="hljs-string">'b'</span>;
    <span class="hljs-keyword">yield</span> <span class="hljs-string">'c'</span>;
  }
  <span class="hljs-keyword">const</span> expected = [<span class="hljs-string">'a'</span>, <span class="hljs-string">'b'</span>, <span class="hljs-string">'c'</span>];
  t.<span class="hljs-title function_">plan</span>(expected.<span class="hljs-property">length</span>);
  <span class="hljs-keyword">const</span> stream = <span class="hljs-title class_">Readable</span>.<span class="hljs-title function_">from</span>(<span class="hljs-title function_">generate</span>());
  stream.<span class="hljs-title function_">on</span>(<span class="hljs-string">'data'</span>, <span class="hljs-function">(<span class="hljs-params">chunk</span>) =></span> {
    t.<span class="hljs-property">assert</span>.<span class="hljs-title function_">strictEqual</span>(chunk, expected.<span class="hljs-title function_">shift</span>());
  });

  stream.<span class="hljs-title function_">on</span>(<span class="hljs-string">'end'</span>, <span class="hljs-function">() =></span> {
    <span class="hljs-title function_">done</span>();
  });
});</code> <button class="copy-button">copy</button></pre>
<h4><code>context.runOnly(shouldRunOnlyTests)</code><span><a class="mark" href="#contextrunonlyshouldrunonlytests" id="contextrunonlyshouldrunonlytests">#</a></span><a aria-hidden="true" class="legacy" id="test_context_runonly_shouldrunonlytests"></a></h4>
<div class="api_metadata">
<span>Added in: v18.0.0, v16.17.0</span>
</div>
<ul>
<li><code>shouldRunOnlyTests</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type">&#x3C;boolean></a> Whether or not to run <code>only</code> tests.</li>
</ul>
<p>If <code>shouldRunOnlyTests</code> is truthy, the test context will only run tests that
have the <code>only</code> option set. Otherwise, all tests are run. If Node.js was not
started with the <a href="cli.html#--test-only"><code>--test-only</code></a> command-line option, this function is a
no-op.</p>
<pre><code class="language-js"><span class="hljs-title function_">test</span>(<span class="hljs-string">'top level test'</span>, <span class="hljs-function">(<span class="hljs-params">t</span>) =></span> {
  <span class="hljs-comment">// The test context can be set to run subtests with the 'only' option.</span>
  t.<span class="hljs-title function_">runOnly</span>(<span class="hljs-literal">true</span>);
  <span class="hljs-keyword">return</span> <span class="hljs-title class_">Promise</span>.<span class="hljs-title function_">all</span>([
    t.<span class="hljs-title function_">test</span>(<span class="hljs-string">'this subtest is now skipped'</span>),
    t.<span class="hljs-title function_">test</span>(<span class="hljs-string">'this subtest is run'</span>, { <span class="hljs-attr">only</span>: <span class="hljs-literal">true</span> }),
  ]);
});</code> <button class="copy-button">copy</button></pre>
<h4><code>context.signal</code><span><a class="mark" href="#contextsignal" id="contextsignal">#</a></span><a aria-hidden="true" class="legacy" id="test_context_signal"></a></h4>
<div class="api_metadata">
<span>Added in: v18.7.0, v16.17.0</span>
</div>
<ul>
<li>Type: <a href="globals.html#class-abortsignal" class="type">&#x3C;AbortSignal></a></li>
</ul>
<p>Can be used to abort test subtasks when the test has been aborted.</p>
<pre><code class="language-js"><span class="hljs-title function_">test</span>(<span class="hljs-string">'top level test'</span>, <span class="hljs-title function_">async</span> (t) => {
  <span class="hljs-keyword">await</span> <span class="hljs-title function_">fetch</span>(<span class="hljs-string">'some/uri'</span>, { <span class="hljs-attr">signal</span>: t.<span class="hljs-property">signal</span> });
});</code> <button class="copy-button">copy</button></pre>
<h4><code>context.skip([message])</code><span><a class="mark" href="#contextskipmessage" id="contextskipmessage">#</a></span><a aria-hidden="true" class="legacy" id="test_context_skip_message"></a></h4>
<div class="api_metadata">
<span>Added in: v18.0.0, v16.17.0</span>
</div>
<ul>
<li><code>message</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type">&#x3C;string></a> Optional skip message.</li>
</ul>
<p>This function causes the test's output to indicate the test as skipped. If
<code>message</code> is provided, it is included in the output. Calling <code>skip()</code> does
not terminate execution of the test function. This function does not return a
value.</p>
<pre><code class="language-js"><span class="hljs-title function_">test</span>(<span class="hljs-string">'top level test'</span>, <span class="hljs-function">(<span class="hljs-params">t</span>) =></span> {
  <span class="hljs-comment">// Make sure to return here as well if the test contains additional logic.</span>
  t.<span class="hljs-title function_">skip</span>(<span class="hljs-string">'this is skipped'</span>);
});</code> <button class="copy-button">copy</button></pre>
<h4><code>context.todo([message])</code><span><a class="mark" href="#contexttodomessage" id="contexttodomessage">#</a></span><a aria-hidden="true" class="legacy" id="test_context_todo_message"></a></h4>
<div class="api_metadata">
<span>Added in: v18.0.0, v16.17.0</span>
</div>
<ul>
<li><code>message</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type">&#x3C;string></a> Optional <code>TODO</code> message.</li>
</ul>
<p>This function adds a <code>TODO</code> directive to the test's output. If <code>message</code> is
provided, it is included in the output. Calling <code>todo()</code> does not terminate
execution of the test function. This function does not return a value.</p>
<pre><code class="language-js"><span class="hljs-title function_">test</span>(<span class="hljs-string">'top level test'</span>, <span class="hljs-function">(<span class="hljs-params">t</span>) =></span> {
  <span class="hljs-comment">// This test is marked as `TODO`</span>
  t.<span class="hljs-title function_">todo</span>(<span class="hljs-string">'this is a todo'</span>);
});</code> <button class="copy-button">copy</button></pre>
<h4><code>context.test([name][, options][, fn])</code><span><a class="mark" href="#contexttestname-options-fn" id="contexttestname-options-fn">#</a></span><a aria-hidden="true" class="legacy" id="test_context_test_name_options_fn"></a></h4>
<div class="api_metadata">
<details class="changelog"><summary>History</summary>
<table>
<tbody><tr><th>Version</th><th>Changes</th></tr>
<tr><td>v18.8.0, v16.18.0</td>
<td><p>Add a <code>signal</code> option.</p></td></tr>
<tr><td>v18.7.0, v16.17.0</td>
<td><p>Add a <code>timeout</code> option.</p></td></tr>
<tr><td>v18.0.0, v16.17.0</td>
<td><p><span>Added in: v18.0.0, v16.17.0</span></p></td></tr>
</tbody></table>
</details>
</div>
<ul>
<li><code>name</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type">&#x3C;string></a> The name of the subtest, which is displayed when reporting
test results. <strong>Default:</strong> The <code>name</code> property of <code>fn</code>, or <code>'&#x3C;anonymous>'</code> if
<code>fn</code> does not have a name.</li>
<li><code>options</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type">&#x3C;Object></a> Configuration options for the subtest. The following
properties are supported:
<ul>
<li><code>concurrency</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type">&#x3C;number></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type">&#x3C;boolean></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Null_type" class="type">&#x3C;null></a> If a number is provided,
then that many tests would run in parallel within the application thread.
If <code>true</code>, it would run all subtests in parallel.
If <code>false</code>, it would only run one test at a time.
If unspecified, subtests inherit this value from their parent.
<strong>Default:</strong> <code>null</code>.</li>
<li><code>only</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type">&#x3C;boolean></a> If truthy, and the test context is configured to run
<code>only</code> tests, then this test will be run. Otherwise, the test is skipped.
<strong>Default:</strong> <code>false</code>.</li>
<li><code>signal</code> <a href="globals.html#class-abortsignal" class="type">&#x3C;AbortSignal></a> Allows aborting an in-progress test.</li>
<li><code>skip</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type">&#x3C;boolean></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type">&#x3C;string></a> If truthy, the test is skipped. If a string is
provided, that string is displayed in the test results as the reason for
skipping the test. <strong>Default:</strong> <code>false</code>.</li>
<li><code>todo</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type">&#x3C;boolean></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type">&#x3C;string></a> If truthy, the test marked as <code>TODO</code>. If a string
is provided, that string is displayed in the test results as the reason why
the test is <code>TODO</code>. <strong>Default:</strong> <code>false</code>.</li>
<li><code>timeout</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type">&#x3C;number></a> A number of milliseconds the test will fail after.
If unspecified, subtests inherit this value from their parent.
<strong>Default:</strong> <code>Infinity</code>.</li>
<li><code>plan</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type">&#x3C;number></a> The number of assertions and subtests expected to be run in the test.
If the number of assertions run in the test does not match the number
specified in the plan, the test will fail.
<strong>Default:</strong> <code>undefined</code>.</li>
</ul>
</li>
<li><code>fn</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type">&#x3C;Function></a> | <a href="https://tc39.es/ecma262/#sec-async-function-constructor" class="type">&#x3C;AsyncFunction></a> The function under test. The first argument
to this function is a <a href="#class-testcontext"><code>TestContext</code></a> object. If the test uses callbacks,
the callback function is passed as the second argument. <strong>Default:</strong> A no-op
function.</li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise" class="type">&#x3C;Promise></a> Fulfilled with <code>undefined</code> once the test completes.</li>
</ul>
<p>This function is used to create subtests under the current test. This function
behaves in the same fashion as the top level <a href="#testname-options-fn"><code>test()</code></a> function.</p>
<pre><code class="language-js"><span class="hljs-title function_">test</span>(<span class="hljs-string">'top level test'</span>, <span class="hljs-title function_">async</span> (t) => {
  <span class="hljs-keyword">await</span> t.<span class="hljs-title function_">test</span>(
    <span class="hljs-string">'This is a subtest'</span>,
    { <span class="hljs-attr">only</span>: <span class="hljs-literal">false</span>, <span class="hljs-attr">skip</span>: <span class="hljs-literal">false</span>, <span class="hljs-attr">concurrency</span>: <span class="hljs-number">1</span>, <span class="hljs-attr">todo</span>: <span class="hljs-literal">false</span>, <span class="hljs-attr">plan</span>: <span class="hljs-number">1</span> },
    <span class="hljs-function">(<span class="hljs-params">t</span>) =></span> {
      t.<span class="hljs-property">assert</span>.<span class="hljs-title function_">ok</span>(<span class="hljs-string">'some relevant assertion here'</span>);
    },
  );
});</code> <button class="copy-button">copy</button></pre>
<h4><code>context.waitFor(condition[, options])</code><span><a class="mark" href="#contextwaitforcondition-options" id="contextwaitforcondition-options">#</a></span><a aria-hidden="true" class="legacy" id="test_context_waitfor_condition_options"></a></h4>
<div class="api_metadata">
<span>Added in: v22.14.0</span>
</div>
<ul>
<li><code>condition</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type">&#x3C;Function></a> | <a href="https://tc39.es/ecma262/#sec-async-function-constructor" class="type">&#x3C;AsyncFunction></a> An assertion function that is invoked
periodically until it completes successfully or the defined polling timeout
elapses. Successful completion is defined as not throwing or rejecting. This
function does not accept any arguments, and is allowed to return any value.</li>
<li><code>options</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type">&#x3C;Object></a> An optional configuration object for the polling operation.
The following properties are supported:
<ul>
<li><code>interval</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type">&#x3C;number></a> The number of milliseconds to wait after an unsuccessful
invocation of <code>condition</code> before trying again. <strong>Default:</strong> <code>50</code>.</li>
<li><code>timeout</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type">&#x3C;number></a> The poll timeout in milliseconds. If <code>condition</code> has not
succeeded by the time this elapses, an error occurs. <strong>Default:</strong> <code>1000</code>.</li>
</ul>
</li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise" class="type">&#x3C;Promise></a> Fulfilled with the value returned by <code>condition</code>.</li>
</ul>
<p>This method polls a <code>condition</code> function until that function either returns
successfully or the operation times out.</p>
</section><section><h3>Class: <code>SuiteContext</code><span><a class="mark" href="#class-suitecontext" id="class-suitecontext">#</a></span><a aria-hidden="true" class="legacy" id="test_class_suitecontext"></a></h3>
<div class="api_metadata">
<span>Added in: v18.7.0, v16.17.0</span>
</div>
<p>An instance of <code>SuiteContext</code> is passed to each suite function in order to
interact with the test runner. However, the <code>SuiteContext</code> constructor is not
exposed as part of the API.</p>
<h4><code>context.filePath</code><span><a class="mark" href="#contextfilepath_1" id="contextfilepath_1">#</a></span><a aria-hidden="true" class="legacy" id="test_context_filepath_1"></a></h4>
<div class="api_metadata">
<span>Added in: v22.6.0</span>
</div>
<p>The absolute path of the test file that created the current suite. If a test
file imports additional modules that generate suites, the imported suites will
return the path of the root test file.</p>
<h4><code>context.name</code><span><a class="mark" href="#contextname_1" id="contextname_1">#</a></span><a aria-hidden="true" class="legacy" id="test_context_name_1"></a></h4>
<div class="api_metadata">
<span>Added in: v18.8.0, v16.18.0</span>
</div>
<p>The name of the suite.</p>
<h4><code>context.signal</code><span><a class="mark" href="#contextsignal_1" id="contextsignal_1">#</a></span><a aria-hidden="true" class="legacy" id="test_context_signal_1"></a></h4>
<div class="api_metadata">
<span>Added in: v18.7.0, v16.17.0</span>
</div>
<ul>
<li>Type: <a href="globals.html#class-abortsignal" class="type">&#x3C;AbortSignal></a></li>
</ul>
<p>Can be used to abort test subtasks when the test has been aborted.</p></section>
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