Type error when using contextlib.asynccontextmanager

I have 2 Python file foo.py and test_foo.py. foo.py:

from contextlib import asynccontextmanager
from typing import AsyncGenerator
class Foo:
    async def bar()->int:
        print("Calling func bar")
        return 1
    async def __aenter__(self):
        return self
    async def __aexit__(self, exc_type, exc, tb):
        return

@asynccontextmanager
async def get_cm() -> AsyncGenerator[Foo, None]:
        yield Foo()

async def call_bar()->int:
    async with get_cm() as foo:
        return await foo.bar()

test_foo.py:

from testslide.dsl import context
from foo import call_bar,Foo
from testslide import StrictMock

module = "foo"

@context
def foo_test(context):
    context.memoize(
        "foo_mock", lambda self: StrictMock(template=Foo, default_context_manager=True)
    )

    @context.before
    async def mock_get_cm(self):
        self.mock_callable(module, "get_cm").to_return_value(
            self.foo_mock
        )
        self.mock_async_callable(self.foo_mock, "bar").to_return_value(3)
    @context.example
    async def test_bar(self):
        self.assertEqual(await call_bar(),3)

When I ran testslide test_foo.py. I hit this type error below.

Failures:

  1) foo test: test bar
    1) TypeError: type of return must be collections.abc.AsyncGenerator; got testslide.strict_mock.FooStrictMock instead: <StrictMock 0x10612BF10 template=foo.Foo testslide_test.py:10>
    Defined at /Users/qxue/testslide_test.py:15
      File ".pyenv/versions/3.8.2/lib/python3.8/asyncio/runners.py", line 43, in run
        return loop.run_until_complete(main)
      File ".pyenv/versions/3.8.2/lib/python3.8/asyncio/base_events.py", line 616, in run_until_complete
        return future.result()
      File "testslide_test.py", line 21, in test_bar
        self.assertEqual(await call_bar(),3)
      File "foo.py", line 20, in call_bar
        async with get_cm() as foo: