Fix unittest.mock.patch and unittest.mock.patch.object when new_callable is not None

[leonarduschen]

This PR fixes multiple issues with unittest.mock.patch and unittest.mock.patch.object

• Both should only accept Callable | None for new_callable, currently Any | None
• When used as context managers, both should return T for new_callable: Callable[..., T], currently they both return Mock | AsyncMock
• When used as decorators to functions:
  • When neither new nor new_callable is given, the function signature should be updated (the mock is passed as last parameter), patch already has the correct behavior but patch.object does not
  • When new_callable is given, same as above, should update function signature. patch already has the correct behavior (by chance, explicit new_callable is not actually handled), but patch.object does not

Addresses #14339

[hauntsaninja]

Would you be interested in adding a few test cases to https://github.com/python/typeshed/blob/main/stdlib/%40tests/test_cases/check_unittest.py ? (the unittest.mock stubs can get a little tricky)

[leonarduschen]

sure!

[github-actions]

According to mypy_primer, this change has no effect on the checked open source code. 🤖🎉

[leonarduschen]

I've updated the original PR description to explain what this PR is fixing

[leonarduschen]

Test result with old implementation

check_unittest.py:190: error: Expression is of type "MagicMock | AsyncMock", not "int"  [assert-type]
check_unittest.py:213: error: Missing positional argument "mock" in call to "obj_f_default_new"  [call-arg]
check_unittest.py:214: error: Missing positional argument "mock" in call to "obj_f_default_new"  [call-arg]
check_unittest.py:214: error: Argument 1 to "obj_f_default_new" has incompatible type "str"; expected "int"  [arg-type]
check_unittest.py:217: error: Missing positional argument "new_callable_ret" in call to "obj_f_explicit_new_callable"  [call-arg]
check_unittest.py:218: error: Missing positional argument "new_callable_ret" in call to "obj_f_explicit_new_callable"  [call-arg]
check_unittest.py:218: error: Argument 1 to "obj_f_explicit_new_callable" has incompatible type "str"; expected "int"  [arg-type]
check_unittest.py:228: error: Expression is of type "MagicMock | AsyncMock", not "int"  [assert-type]

This agrees with the upated PR description:

This PR fixes multiple issues with unittest.mock.patch and unittest.mock.patch.object

• Both should only accept Callable | None for new_callable, currently Any | None

• When used as context managers, both should return T for new_callable: Callable[..., T], currently they both return Mock | AsyncMock

• When used as decorators to functions:

  • When neither new nor new_callable is given, the function signature should be updated (the mock is passed as last parameter), patch already has the correct behavior but patch.object does not
  • When new_callable is given, same as above, should update function signature. patch already has the correct behavior (by chance, explicit new_callable is not actually handled), but patch.object does not

[srittau]

Thanks!