The expectation is that the __module__ attribute for a patched function should persist after patching.

Minimal test case is attached. Simply run pytest in a venv with the files.

Output:
def test_zxc():
        with mock.patch.object(mymodule, 'asd', side_effect=mymodule.asd, autospec=True) as spy_asd:
>           assert spy_asd.__module__ == 'mymodule'
E           AssertionError: assert None == 'mymodule'
E            +  where None = <function asd at 0x7fe4cd6fd620>.__module__

test_mymodule.py:8: AssertionError

Originally reported at https://github.com/pytest-dev/pytest-mock/issues/146 before it was determined this was a unittest.mock issue.

Happens on both Python 2.7 and 3.7. Probably not really tied to a specific Python version and more of mock library issue.

My local venv:
Python 3.7.2
pytest 4.4.1