Fix failing unit tests

[dchiquito]

Fix failing unit tests

[dchiquito]

The test_import and test_importlib bugs should be fixed by #5192

[dchiquito]

The test_with bugs should be fixed by #5203

[dchiquito]

The test_typing errors are caused by this test in test_typing.py:

class ProtocolTests(BaseTestCase):
    ...
    def test_protocols_bad_subscripts(self):
        T = TypeVar('T')
        S = TypeVar('S')
        with self.assertRaises(TypeError):
            class P(Protocol[T, T]): pass
        with self.assertRaises(TypeError):
            class P(Protocol[int]): pass
        with self.assertRaises(TypeError):
            class P(Protocol[T], Protocol[S]): pass
        with self.assertRaises(TypeError):
            class P(typing.Mapping[T, S], Protocol[T]): pass # <- specifically this line

This specific line is corrupting the typing.Mapping object in some way that renders the unittest.mock module unimportable. I suspect that the line in question Protocol.__init_subclass__ sets __subclasshook__ before it fails, which is then called somehow in unittest.mock.

[dchiquito]

The test_mmap/test_os failures should be resolved by #5204

[dchiquito]

The test_typing errors should be resolved by #5207

[dchiquito]

Everything seems to have been resolved.

[youknowone]

Thank you so much! This series is really helpful 😄