Use asyncio (cooperative multitasking) to run your I/O bound test suite efficiently and quickly.

import asyncio

import pytest

@pytest.mark.asyncio_cooperative
async def test_a():
    await asyncio.sleep(2)


@pytest.mark.asyncio_cooperative
async def test_b():
    await asyncio.sleep(2)

========== 2 passed in 2.05 seconds ==========

Quickstart

pip install pytest-asyncio-cooperative

Compatibility

pytest-asyncio is NOT compatible with this plugin. Please uninstall pytest-asyncio or pass this flag to pytest -p no:asyncio

Fixtures

It's recommended that async tests use async fixtures.

import asyncio
import pytest


@pytest.fixture
async def my_fixture():
    await asyncio.sleep(2)
    yield "XXX"
    await asyncio.sleep(2)


@pytest.mark.asyncio_cooperative
async def test_a(my_fixture):
    await asyncio.sleep(2)
    assert my_fixture == "XXX"

Goals

• Reduce the total run time of I/O bound test suites via cooperative multitasking
• Reduce system resource usage via cooperative multitasking

Pros

• An I/O bound test suite will run faster (ie. individual tests will take just as long. The total runtime of the entire test suite will be faster)
• An I/O bound test suite will use less system resources (ie. only a single thread is used)

Cons

• Order of tests is not guaranteed (ie. some blocking operations might taken longer and affect the order of test results)
• Tests MUST be isolated from each other (ie. NO shared resources, NO mock.patch). However, note that locks can be used to ensure isolation.
• There is NO parallelism, CPU bound tests will NOT get a performance benefit

Mocks & Shared Resources

When using mocks and shared resources cooperative multitasking means tests could have race conditions.

In this case you can use locks:

import asyncio
import pytest
from pytest_asyncio_cooperative import Lock

my_lock = Lock()

@pytest.fixture(scope="function")
async def lock():
    async with my_lock():
        yield

@pytest.mark.asyncio_cooperative
async def test_a(lock, mocker):
    await asyncio.sleep(2)
    mocker.patch("service.http.on_handler")
    access_shared_resource()
    assert my_fixture == "XXX"

@pytest.mark.asyncio_cooperative
async def test_b(lock, mocker):
    await asyncio.sleep(2)
    mocker.patch("service.http.on_handler")
    access_shared_resource()
    assert my_fixture == "XXX"

In the above example it's important to put the lock fixture on the far left-hand side to ensure mutual exclusivity.

Timeouts

Tests are automatically cancelled after a timeout of 600s. You can change this with the --asyncio-task-timeout option or by adding an asyncio_task_timeout entry to your pytest.ini file.

Maximum Asynchronous Tasks

Sometimes you want to limit the number of tasks running concurrently. You can set a maximum with the --max-asyncio-tasks option by adding a max_asyncio_tasks entry to your pytest.ini file.