asyncio event loops

pytest-asyncio runs each test item in its own asyncio event loop. The loop can be accessed via the event_loop fixture, which is automatically requested by all async tests.

async def test_provided_loop_is_running_loop(event_loop):
    assert event_loop is asyncio.get_running_loop()

You can think of event_loop as an autouse fixture for async tests.

Test discovery modes

Pytest-asyncio provides two modes for test discovery, strict and auto.

Strict mode

In strict mode pytest-asyncio will only run tests that have the asyncio marker and will only evaluate async fixtures decorated with @pytest_asyncio.fixture. Test functions and fixtures without these markers and decorators will not be handled by pytest-asyncio.

This mode is intended for projects that want so support multiple asynchronous programming libraries as it allows pytest-asyncio to coexist with other async testing plugins in the same codebase.

Pytest automatically enables installed plugins. As a result pytest plugins need to coexist peacefully in their default configuration. This is why strict mode is the default mode.

Auto mode

In auto mode pytest-asyncio automatically adds the asyncio marker to all asynchronous test functions. It will also take ownership of all async fixtures, regardless of whether they are decorated with @pytest.fixture or @pytest_asyncio.fixture.

This mode is intended for projects that use asyncio as their only asynchronous programming library. Auto mode makes for the simplest test and fixture configuration and is the recommended default.

If you intend to support multiple asynchronous programming libraries, e.g. asyncio and trio, strict mode will be the preferred option.