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<div class="section" id="getting-started-with-mock">
<h1>Getting Started with Mock<a class="headerlink" href="#getting-started-with-mock" title="Permalink to this headline">¶</a></h1>
<span class="target" id="index-10"></span><div class="section" id="using-mock">
<h2>Using Mock<a class="headerlink" href="#using-mock" title="Permalink to this headline">¶</a></h2>
<p><tt class="docutils literal"><span class="pre">Mock</span></tt> objects can be used for:</p>
<ul class="simple">
<li>Patching methods</li>
<li>Recording method calls on objects</li>
</ul>
<div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="kn">from</span> <span class="nn">mock</span> <span class="kn">import</span> <span class="n">Mock</span>
<span class="gp">>>> </span><span class="n">real</span> <span class="o">=</span> <span class="n">ProductionClass</span><span class="p">()</span>
<span class="gp">>>> </span><span class="n">real</span><span class="o">.</span><span class="n">method</span> <span class="o">=</span> <span class="n">Mock</span><span class="p">()</span>
<span class="go">>>></span>
<span class="gp">>>> </span><span class="n">real</span><span class="o">.</span><span class="n">method</span><span class="p">(</span><span class="mf">3</span><span class="p">,</span> <span class="mf">4</span><span class="p">,</span> <span class="mf">5</span><span class="p">,</span> <span class="n">key</span><span class="o">=</span><span class="s">'value'</span><span class="p">)</span>
<span class="go"><mock.Mock object at 0x...></span>
<span class="go">>>></span>
</pre></div>
</div>
<p>Once the mock has been used it has methods and attributes that allow you to make assertions about how it has been used:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="n">real</span><span class="o">.</span><span class="n">method</span><span class="o">.</span><span class="n">assert_called_with</span><span class="p">(</span><span class="mf">3</span><span class="p">,</span> <span class="mf">4</span><span class="p">,</span> <span class="mf">5</span><span class="p">,</span> <span class="n">key</span><span class="o">=</span><span class="s">'value'</span><span class="p">)</span>
<span class="gp">>>> </span><span class="n">real</span><span class="o">.</span><span class="n">method</span><span class="o">.</span><span class="n">called</span>
<span class="go">True</span>
<span class="gp">>>> </span><span class="n">real</span><span class="o">.</span><span class="n">method</span><span class="o">.</span><span class="n">call_args</span>
<span class="go">((3, 4, 5), {'key': 'value'})</span>
<span class="go">>>></span>
</pre></div>
</div>
<p>Mocks also record calls made to attributes, their ‘child’ attributes:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="n">mock</span> <span class="o">=</span> <span class="n">Mock</span><span class="p">()</span>
<span class="gp">>>> </span><span class="n">mock</span><span class="o">.</span><span class="n">something</span><span class="p">()</span>
<span class="go"><mock.Mock object at 0x...></span>
<span class="gp">>>> </span><span class="n">mock</span><span class="o">.</span><span class="n">method_calls</span>
<span class="go">[('something', (), {})]</span>
</pre></div>
</div>
<p>You can also create Mock objects that behave like the class they are intended to mock. This is done with the <tt class="docutils literal"><span class="pre">spec</span></tt> keyword argument, which either takes a list of strings describing the attributes that the mock should have - or you can pass in the object (class or instance) that you are mocking out. Attempting to access an attribute on the mock that isn’t in the spec will raise an <tt class="docutils literal"><span class="pre">AttributeError</span></tt>.</p>
<div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="n">mock</span> <span class="o">=</span> <span class="n">Mock</span><span class="p">(</span><span class="n">spec</span><span class="o">=</span><span class="p">[</span><span class="s">'something'</span><span class="p">])</span>
<span class="gp">>>> </span><span class="n">mock</span><span class="o">.</span><span class="n">something</span><span class="p">()</span>
<span class="go"><mock.Mock object at 0x...></span>
<span class="gp">>>> </span><span class="n">mock</span><span class="o">.</span><span class="n">something_else</span><span class="p">()</span>
<span class="gt">Traceback (most recent call last):</span>
<span class="c">...</span>
<span class="nc">AttributeError</span>: <span class="n-Identifier">object has no attribute 'something_else'</span>
</pre></div>
</div>
<p>There are various ways of configuring the mock, including setting return values
on the mock and its methods. A useful attribute is <tt class="docutils literal"><span class="pre">side_effect</span></tt>. If you set
this to an exception class or instance then the exception will be raised when
the mock is called. If you set it to a callable then it will be called whenever
the mock is called. This allows you to do things like return members of a
sequence from repeated calls:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="n">mock</span> <span class="o">=</span> <span class="n">Mock</span><span class="p">()</span>
<span class="gp">>>> </span><span class="n">mock</span><span class="o">.</span><span class="n">side_effect</span> <span class="o">=</span> <span class="ne">Exception</span><span class="p">(</span><span class="s">'Boom!'</span><span class="p">)</span>
<span class="gp">>>> </span><span class="n">mock</span><span class="p">()</span>
<span class="gt">Traceback (most recent call last):</span>
<span class="c">...</span>
<span class="nc">Exception</span>: <span class="n-Identifier">Boom!</span>
<span class="gp">>>> </span><span class="n">results</span> <span class="o">=</span> <span class="p">[</span><span class="mf">1</span><span class="p">,</span> <span class="mf">2</span><span class="p">,</span> <span class="mf">3</span><span class="p">]</span>
<span class="gp">>>> </span><span class="k">def</span> <span class="nf">side_effect</span><span class="p">(</span><span class="o">*</span><span class="n">args</span><span class="p">,</span> <span class="o">**</span><span class="n">kwargs</span><span class="p">):</span>
<span class="gp">... </span> <span class="k">return</span> <span class="n">results</span><span class="o">.</span><span class="n">pop</span><span class="p">()</span>
<span class="gp">...</span>
<span class="gp">>>> </span><span class="n">mock</span><span class="o">.</span><span class="n">side_effect</span> <span class="o">=</span> <span class="n">side_effect</span>
<span class="gp">>>> </span><span class="n">mock</span><span class="p">(),</span> <span class="n">mock</span><span class="p">(),</span> <span class="n">mock</span><span class="p">()</span>
<span class="go">(3, 2, 1)</span>
</pre></div>
</div>
</div>
<div class="section" id="sentinel">
<h2>Sentinel<a class="headerlink" href="#sentinel" title="Permalink to this headline">¶</a></h2>
<p><tt class="docutils literal"><span class="pre">sentinel</span></tt> is a useful object for providing unique objects in your tests:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="kn">from</span> <span class="nn">mock</span> <span class="kn">import</span> <span class="n">sentinel</span>
<span class="gp">>>> </span><span class="n">real</span> <span class="o">=</span> <span class="n">ProductionClass</span><span class="p">()</span>
<span class="gp">>>> </span><span class="n">real</span><span class="o">.</span><span class="n">method</span> <span class="o">=</span> <span class="n">Mock</span><span class="p">()</span>
<span class="go">>>></span>
<span class="gp">>>> </span><span class="n">real</span><span class="o">.</span><span class="n">method</span><span class="o">.</span><span class="n">return_value</span> <span class="o">=</span> <span class="n">sentinel</span><span class="o">.</span><span class="n">return_value</span>
<span class="gp">>>> </span><span class="n">real</span><span class="o">.</span><span class="n">method</span><span class="p">()</span>
<span class="go"><SentinelObject "return_value"></span>
</pre></div>
</div>
</div>
<div class="section" id="patch-decorators">
<h2>Patch Decorators<a class="headerlink" href="#patch-decorators" title="Permalink to this headline">¶</a></h2>
<p>There are also decorators for doing module and class level patching. As modules and classes are effectively globals any patching has to be undone (or it persists into other tests). These decorators do the unpatching for you, making it easier to test with module and class level patching.</p>
<p>The two decorators are ‘patch’ and ‘patch_object’. ‘patch’ takes a single string, of the form <tt class="docutils literal"><span class="pre">package.module.Class.attribute</span></tt> to specify the attribute you are patching. It also optionally takes a value that you want the attribute (or class or whatever) to be replaced with. ‘patch_object’ takes an object and the name of the attribute you would like patched, plus optionally the value to patch it with.</p>
<div class="highlight-python"><div class="highlight"><pre><span class="n">original</span> <span class="o">=</span> <span class="n">SomeClass</span><span class="o">.</span><span class="n">attribute</span>
<span class="nd">@patch_object</span><span class="p">(</span><span class="n">SomeClass</span><span class="p">,</span> <span class="s">'attribute'</span><span class="p">,</span> <span class="n">sentinel</span><span class="o">.</span><span class="n">Attribute</span><span class="p">)</span>
<span class="k">def</span> <span class="nf">test</span><span class="p">():</span>
<span class="bp">self</span><span class="o">.</span><span class="n">assertEquals</span><span class="p">(</span><span class="n">SomeClass</span><span class="o">.</span><span class="n">attribute</span><span class="p">,</span> <span class="n">sentinel</span><span class="o">.</span><span class="n">Attribute</span><span class="p">,</span> <span class="s">"class attribute not patched"</span><span class="p">)</span>
<span class="n">test</span><span class="p">()</span>
<span class="bp">self</span><span class="o">.</span><span class="n">assertEquals</span><span class="p">(</span><span class="n">SomeClass</span><span class="o">.</span><span class="n">attribute</span><span class="p">,</span> <span class="n">original</span><span class="p">,</span> <span class="s">"attribute not restored"</span><span class="p">)</span>
<span class="nd">@patch</span><span class="p">(</span><span class="s">'Package.Module.attribute'</span><span class="p">,</span> <span class="n">sentinel</span><span class="o">.</span><span class="n">Attribute</span><span class="p">)</span>
<span class="k">def</span> <span class="nf">test</span><span class="p">():</span>
<span class="s">"do something"</span>
<span class="n">test</span><span class="p">()</span>
</pre></div>
</div>
<p>If you don’t want to call the decorated test function yourself, you can add <tt class="docutils literal"><span class="pre">apply</span></tt> as a decorator on top:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="nd">@apply</span>
<span class="nd">@patch</span><span class="p">(</span><span class="s">'Package.Module.attribute'</span><span class="p">,</span> <span class="n">sentinel</span><span class="o">.</span><span class="n">Attribute</span><span class="p">)</span>
<span class="k">def</span> <span class="nf">test</span><span class="p">():</span>
<span class="s">"do something"</span>
</pre></div>
</div>
<p>(Note that this leaves test == None)</p>
<p>A nice pattern is to actually decorate test methods themselves:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="nd">@patch</span><span class="p">(</span><span class="s">'Package.Module.attribute'</span><span class="p">,</span> <span class="n">sentinel</span><span class="o">.</span><span class="n">Attribute</span><span class="p">)</span>
<span class="k">def</span> <span class="nf">testMethod</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
<span class="s">"do something"</span>
</pre></div>
</div>
<p>If you want to patch with a Mock, you can use <tt class="docutils literal"><span class="pre">patch</span></tt> with only one argument (or <tt class="docutils literal"><span class="pre">patch_object</span></tt> with two arguments). The mock will be created for you and passed into the test function / method:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="nd">@patch</span><span class="p">(</span><span class="s">'Package.Module.Class'</span><span class="p">)</span>
<span class="k">def</span> <span class="nf">testMethod</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">mMckClass</span><span class="p">):</span>
<span class="s">"do something"</span>
</pre></div>
</div>
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<li><a class="reference external" href="#using-mock">Using Mock</a></li>
<li><a class="reference external" href="#sentinel">Sentinel</a></li>
<li><a class="reference external" href="#patch-decorators">Patch Decorators</a></li>
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