Merge pull request #1079 from python-cmd2/autospec_doc_updates

Update autospec mock documentation

Author: kotfu

docs/testing.rst

@@ -26,21 +26,45 @@ Mocking
 .. _python_mock_patch:
    https://docs.python.org/3/library/unittest.mock.html#patch
 
-If you need to mock anything in your cmd2 application, and most specifically in sub-classes of :class:`~cmd2.Cmd` or
-:class:`~cmd2.command_definition.CommandSet`, you must use `Autospeccing <python_mock_autospeccing_>`_,
-`spec=True <python_mock_patch_>`_, or whatever equivalant 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 <python_mock_autospeccing_>`_ or `spec=True <python_mock_patch_>`_
-enabled.
-
-Example of spec=True
-~~~~~~~~~~~~~~~~~~~~
+If you need to mock anything in your cmd2 application, and most specifically in
+sub-classes of :class:`~cmd2.Cmd` or
+:class:`~cmd2.command_definition.CommandSet`, you must use `Autospeccing
+<python_mock_autospeccing_>`_, `spec=True <python_mock_patch_>`_, or whatever
+equivalant 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
+<python_mock_autospeccing_>`_ or `spec=True <python_mock_patch_>`_ enabled.
+
+If you don't have autospeccing on, your unit tests will failing 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
+~~~~~~~~
+
 .. code-block:: python
 
     def test_mocked_methods():
         with mock.patch.object(MockMethodApp, 'foo', spec=True):
             cli = MockMethodApp()
+
+Another one using `pytest-mock <https://pypi.org/project/pytest-mock/>`_ to
+provide a ``mocker`` fixture:
+
+.. code-block:: python
+
+   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