Add async_stub method

[PerchunPak]

Which actually the same as stub but creates async stub.

[PerchunPak]

[nicoddemus]

Thanks a lot @PerchunPak for the contribution, sorry about the delay.

There are some things that need fixing:

1. Can you take a look at the test failures? Seems like we have to put a guard around the definition of async_stub on the Python versions that don't support it.
2. Could you add a very simple test to TestMockerStub that just calls async_stub and ensures it is an instance of unittest.mock.AsyncMock? This is just to avoid future regressions. The test needs to be skipped on unsupported Python versions.
3. Finally could add a quick changelog entry for this, under a new session 3.8.0 (unreleased)?

Thanks again!

[PerchunPak]

Can you take a look at the test failures? Seems like we have to put a guard around the definition of async_stub on the Python versions that don't support it.

Can't imagine how, seems like mock_module.AsyncMock will not work with type checkers, so how this could be done?
Maybe import standalone mock module in if TYPE_CHECKING: block?

[PerchunPak]

I thought about variant like this, but users also can use standalone mock package, which have AsyncMock class.

[nicoddemus]

Sorry I should have mentioned, but mypy supports sys.version_info checks. 👍

[PerchunPak]

Sorry I should have mentioned, but mypy supports sys.version_info checks. 👍

Yes, but how about runtime? Yes unittest.mock doesn't have AsyncMock in py3.7, but mock have.

[nicoddemus]

I'm OK with only supporting AsyncMock for Python 3.8+, or is this something you need in Python 3.7?

[PerchunPak]

I'm OK with only supporting AsyncMock for Python 3.8+, or is this something you need in Python 3.7?

No, just you support both (unittest.mock and mock), it's strange that you breaking this support here.

[nicoddemus]

Hmm an alternative would be then:

if sys.version_info[:2] >= (3, 8):
    AsyncMockType = unittest.mock.AsyncMock
else:
    AsyncMockType = mock.AsyncMock

at the top of the file, then use AsyncMockType in the annotation. If the above does not work, then AsyncMockType = Any for Python 3.7 is a good compromise.

[nicoddemus]

Awesome, thanks a lot for the contribution and patience! 🙇