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# External Test Plugin
## Overview
The [External Test Plugin](https://github.com/python-cmd2/cmd2/tree/master/plugins/ext_test) supports testing of a cmd2 application by exposing access to cmd2 commands with the same context as from within a cmd2 [Python Script](../features/scripting.md#python-scripts). This interface captures `stdout`, `stderr`, as well as any application-specific data returned by the command. This also allows for verification of an application's support for [Python Scripts](../features/scripting.md#python-scripts) and enables the cmd2 application to be tested as part of a larger system integration test.
## Example cmd2 Application
The following short example shows how to mix in the external test plugin to create a fixture for testing your cmd2 application.
Define your cmd2 application
```py
import cmd2
class ExampleApp(cmd2.Cmd):
"""An class to show how to use a plugin"""
def __init__(self, *args, **kwargs):
# gotta have this or neither the plugin or cmd2 will initialize
super().__init__(*args, **kwargs)
def do_something(self, arg):
self.last_result = 5
self.poutput('this is the something command')
```
## Defining the test fixture
In your test, define a fixture for your cmd2 application
```py
import cmd2_ext_test
import pytest
class ExampleAppTester(cmd2_ext_test.ExternalTestMixin, ExampleApp):
def __init__(self, *args, **kwargs):
# gotta have this or neither the plugin or cmd2 will initialize
super().__init__(*args, **kwargs)
@pytest.fixture
def example_app():
app = ExampleAppTester()
app.fixture_setup()
yield app
app.fixture_teardown()
```
## Writing Tests
Now write your tests that validate your application using the `cmd2_ext_test.ExternalTestMixin.app_cmd` function to access the cmd2 application's commands. This allows invocation of the application's commands in the same format as a user would type. The results from calling a command matches what is returned from running an python script with cmd2's [run_pyscript](../features/builtin_commands.md#run_pyscript) command, which provides `stdout`, `stderr`, and the command's result data.
```py
from cmd2 import CommandResult
def test_something(example_app):
# execute a command
out = example_app.app_cmd("something")
# validate the command output and result data
assert isinstance(out, CommandResult)
assert str(out.stdout).strip() == 'this is the something command'
assert out.data == 5
```
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