Mocks can no longer be used as the specs for other Mocks. As a result, an
already-mocked object cannot have an attribute mocked using ``autospec=True``
or be the subject of a ``create_autospec(...)`` call. This can uncover bugs in
tests since these Mock-derived Mocks will always pass certain tests (e.g.
:func:`isinstance`) and builtin assert functions (e.g. assert_called_once_with)
will unconditionally pass.
