When an `unittest.mock.create_autospec(Obj, instance=True)` is used, and said Obj implements the `__call__(self, ...)` function, the mocked instance of it will take the full function signature including the `self` argument.
This will then cause an issue when `assert_called_once_with()` or `assert_called_with()` is used. Those two assertions will fail regardless if the arguments used were correct or not. The error message will contain the error: `TypeError: missing a required argument: 'self'`
Here an example of this issue happening
```
from unittest import mock
def Foo(object):
def __call__(self, a):
pass
def bar(self, b):
```This is to just compare it with a regular function.```
pass
foo_mock = mock.create_autospec(Foo, instance=True)
foo_mock(a=1)
foo_mock.assert_called_once_with(a=1)
```
In the example above, the assertion will then fail and raise an error even though the assertion should be correct.
upon inspecting further to understand the issue, this is because `foo_mock._spec_signature` will be `<Signature (self, a)>`.
The existence of `self` in `foo_mock._spec_signature` will cause this error.
As compared to the method `foo_mock.bar._spec_signature`, it will only be `<Signature (b)>`.
The reason for me posting this issue is that development with the Keras library heavily uses __call__ in their API and therefore it is hard to mock the APIs if such issue exists. One work around would be iterating through its `called_args_list`.
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