pytest-asyncio-cooperative

0.40.0 verified Fri May 01 auth: no python

A pytest plugin that runs all async tests cooperatively using a single event loop, avoiding event loop conflicts and improving performance. Current version: 0.40.0, requires Python >=3.8. Released under MIT license; maintenance cadence is irregular.

pip install pytest-asyncio-cooperative

Common errors

error RuntimeError: There is no current event loop in thread 'MainThread' ↓

cause Missing session-scoped event_loop fixture.

fix

Add a session-scoped event_loop fixture in conftest.py: @pytest.fixture(scope="session") def event_loop(): loop = asyncio.new_event_loop() asyncio.set_event_loop(loop) yield loop loop.close()

error Fixture 'event_loop' cannot be a session-scoped fixture because it is defined in a non-top-level conftest ↓

cause The event_loop fixture is defined in a conftest.py inside a subpackage, but pytest-asyncio-cooperative expects it at the root conftest or the test directory.

fix

Move the event_loop fixture to the root conftest.py (or ensure the conftest.py is in the top-level test directory).

error AttributeError: module 'pytest' has no attribute 'mark' ↓

cause Attempting to import pytest.mark without the marker being registered.

fix

Ensure pytest-asyncio-cooperative is installed and the conftest.py is found. The marker is automatically registered when the plugin is active.

error DeprecationWarning: The 'event_loop' fixture is deprecated ↓

cause Using an older version of pytest-asyncio that suppresses the warning, but pytest-asyncio-cooperative may use the old fixture pattern.

fix

Upgrade pytest-asyncio and pytest-asyncio-cooperative to latest versions. If the warning persists, use scope='session' event_loop fixture as recommended.

Warnings

gotcha The marker is @pytest.mark.asyncio_cooperative, not @pytest.mark.asyncio. Using the wrong marker will run tests in isolated loops and may cause event loop conflicts. ↓

fix Use @pytest.mark.asyncio_cooperative instead of @pytest.mark.asyncio.

gotcha The plugin requires a session-scoped event_loop fixture. If you forget to define it, you may get 'RuntimeError: There is no current event loop in thread'. ↓

fix Define a session-scoped event_loop fixture in conftest.py that creates a new event loop.

gotcha Tests that call loop.run_until_complete() or create sub-loops may interfere with the shared loop. Avoid mixing cooperative tests with those that manage their own loops. ↓

fix Ensure all async tests within the session use the same event loop; do not create new loops manually.

Imports

pytest.mark.asyncio_cooperative

from pytest_asyncio_cooperative import pytest_configure

pytest_configure

wrong

import pytest_asyncio_cooperative

correct

from pytest_asyncio_cooperative import pytest_configure

Not needed; plugin auto-registers.

Quickstart

Basic setup: define a session-scoped event_loop fixture (if not using async fixtures) and mark tests with @pytest.mark.asyncio_cooperative.

# conftest.py
import asyncio
import sys

@pytest.fixture(scope="session")
def event_loop():
    loop = asyncio.new_event_loop()
    asyncio.set_event_loop(loop)
    yield loop
    loop.close()

# test_async.py
import pytest

@pytest.mark.asyncio_cooperative
async def test_async_example():
    await asyncio.sleep(0.1)
    assert True