Lock pytest-asyncio version at >=0.17 <0.19. This is because pytest-asyncio changes how it handles async fixture since version 0.16. Prior to 0.16, pytest.fixture was treated as async fixture automatically. After 0.16, pytest_asyncio.fixture need to be used on async fixtures. This rule gets enforced after 0.19, which is why we cannot use 0.19 for now. For detail, see https://github.com/pytest-dev/pytest-asyncio readme.