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# Testing

## Overview

This covers special considerations when writing unit or integration tests for a cmd2 application.

## Testing Commands

We encourage `cmd2` application developers to look at the cmd2 tests for examples of how to perform unit and integration testing of `cmd2` commands. There are various helpers that will do things like capture and return stdout, stderr, and command-specific result data.

## Mocking

If you need to mock anything in your cmd2 application, and most specifically in sub-classes of cmd2.Cmd or cmd2.CommandSet, you must use Autospeccing, spec=True, or whatever equivalent is provided in the mocking library you're using.

In order to automatically load functions as commands, `cmd2` performs a number of reflection calls to look up attributes of classes defined in your cmd2 application. Many mocking libraries will automatically create mock objects to match any attribute being requested, regardless of whether they're present in the object being mocked. This behavior can incorrectly instruct cmd2 to treat a function or attribute as something it needs to recognize and process. To prevent this, you should always mock with Autospeccing or spec=True enabled. If you don't have autospeccing on, your unit tests will fail with an error message like:

    cmd2.exceptions.CommandSetRegistrationError: Subcommand
    <MagicMock name='cmdloop.subcommand_name' id='4506146416'> is not valid: must be a string.
    Received <class 'unittest.mock.MagicMock'> instead

## Examples

    def test*mocked_methods():
       with mock.patch.object(MockMethodApp, 'foo', spec=True):
          cli = MockMethodApp()

Another one using pytest-mock to provide a `mocker` fixture:

    def test_mocked_methods2(mocker):
       mock_cmdloop = mocker.patch("cmd2.Cmd.cmdloop", autospec=True)
       cli = cmd2.Cmd()
       cli.cmdloop()
       assert mock_cmdloop.call_count == 1