If you are trying to use AsyncMock to mock a coroutine that returns awaitable objects, AsyncMock awaits on those objects instead of returning them as is. Example:  mock = AsyncMock(return_value=asyncio.Future())  v = await mock()  # blocks on trying to await the futureExpected:  mock = AsyncMock(return_value=asyncio.Future())  v = await mock()  assert isisnstance(v, asyncio.Future)This problem affects side_effects and wraps.

New changeset046442d02bcc6e848e71e93e47f6cde9e279e993 by Lisa Roach (Jason Fried) in branch 'master':bpo-38857: AsyncMock fix for awaitable values and StopIteration fix [3.8] (GH-17269)https://github.com/python/cpython/commit/046442d02bcc6e848e71e93e47f6cde9e279e993

New changesetb2744c1be73f5af0d2dc4b952389efc90c8de94e by Andrew Svetlov (Lisa Roach) in branch '3.8':[3.8]bpo-38857: AsyncMock fix for awaitable values and StopIteration fix [3.8] (GH-17269) (#17304)https://github.com/python/cpython/commit/b2744c1be73f5af0d2dc4b952389efc90c8de94e

I think this deserves discussion :)On one hand, it's a welcome change, on another it's kind of a regression.Up until 3.8, our tests used to look like this:---# code under testasync def foo():    return await bar()# testasync def helper(value):    return valueasync def test_foo():    with patch("bar", return_value=helper(42)):        assert await foo() == 42---I feel that the default class `patch()` uses for `new` has crept in too quietly in 3.8.At the same time, `helper` was only used because there was no `AsyncMock`.(or at times, a 3rd party library, `asynctest` was used).So, on one hand, it's a bit of a regression, but on the other, looking ahead, I would really like `unittest.mock` to do the right thing.Can we have it both ways? If not, what way is a better way?

Its not possible to have it both ways.  Also it stinks too much of trying to guess. The root of your issue is you want a normal MagicMock not an AsyncMock. Its the automatic behavior of patch to pick AsyncMock vs MagicMock that is the heart of your issue.  This bug fix doesn't involve that behavior at all, and AsyncMock was measurably broken without the fix, in an unavoidable way.  Your breakage is avoidable by changes to how you patch.   with patch("bar", return_value=42)To still do it the old way you would have to pass new_callable=MagicMock to patch.

Thank you for explanation, Jason!I guess that the bug report and the patch were too technical for me to understand 😅I'm happy with the behaviour in Python 3.8.1 and now I know it's going to stay, I'll just change the tests in our code base.