Unclear error mocking a class and asserting called with about mock HOT 2 CLOSED

This package is a rolling backport of unittest.mock.
As such, any problems you encounter most likely need to be fixed upstream.

Please can you try and reproduce the problem on the latest release of Python 3, including alphas, and replace any import from mock with ones from unittest.mock.

If the issue still occurs, then please report upstream through https://github.com/python/cpython/issues as it will need to be fixed there so that it can be backported here and released to you.

If not, reply with what you find out and we can re-open this issue.

from mock.

I can confirm that the issue exists in master branch of CPython. The issue is that using spec only checks for invalid attribute access and not signatures. So MagicMock(AClass) uses AClass as spec and checks for only attribute access on the mock allowing invalid attributes but assert_ helpers check for signature since Python 3.4. There was a proposal to make spec also do signature checking but it will break backwards compatibility due to strict checks and auto spec is also expensive since it would also apply it for methods. I would suggest using create_autospec since that will check for signature too catching these issues earlier.

from unittest.mock import MagicMock, create_autospec

class AClass:

    def __init__(self, a, b=2):
        pass


def test_mock(kwargs):
    mock_a_class = create_autospec(AClass)
    mock_a_class(**kwargs)
    mock_a_class.assert_called_once_with(**kwargs)

test_mock({})
test_mock({'c': 1, 'a': 2})

python /tmp/foo.py
Traceback (most recent call last):
  File "/tmp/foo.py", line 14, in <module>
    test_mock({})
  File "/tmp/foo.py", line 11, in test_mock
    mock_a_class(**kwargs)
  File "/usr/lib/python3.10/unittest/mock.py", line 1102, in __call__
    self._mock_check_sig(*args, **kwargs)
  File "/usr/lib/python3.10/unittest/mock.py", line 123, in checksig
    sig.bind(*args, **kwargs)
  File "/usr/lib/python3.10/inspect.py", line 3179, in bind
    return self._bind(args, kwargs)
  File "/usr/lib/python3.10/inspect.py", line 3094, in _bind
    raise TypeError(msg) from None
TypeError: missing a required argument: 'a'

python/cpython#74772

from mock.