In the following code:

async def test1():
    assert Fail

@pytest.mark.asyncio
async def test2():
    assert Fail

• test1 is silently skipped and marked as successful.
• test2 follows the same fate if pytest-asyncio is not installed.

Both use cases can be very easily triggered by distraction in real life; the sensible behaviour should be that both tests fail no matter what:

• Using the @pytest.mark.asyncio decorator without pytest-asyncio installed should cause an error
• An error should be raised if a test function returns a coroutine