Async fixtures (pytest-asyncio)

Introduction

Async fixtures help prepare things that need to wait for some time or work with async code before tests run.

When you need to set up a database connection that uses async calls.

When you want to prepare a web server or client that works asynchronously.

When you have to load data or resources using async functions before tests.

When cleaning up resources after async operations in tests.

When testing code that uses async functions and you want to share setup steps.

Syntax

PyTest

import pytest

@pytest.fixture
async def my_async_fixture():
    # setup code here
    yield resource
    # teardown code here

Use async def to define async fixtures.

Use yield to provide the fixture value and then run cleanup after the test.

Examples

This fixture waits for setup, gives 'ready' to the test, then cleans up asynchronously.

PyTest

import pytest

@pytest.fixture
async def sample_fixture():
    await some_async_setup()
    yield 'ready'
    await some_async_cleanup()

This fixture gets a number asynchronously and provides it to tests.

PyTest

import pytest

@pytest.fixture
async def number_fixture():
    number = await get_async_number()
    yield number

Sample Program

This test uses an async fixture that waits a bit before and after the test. It prints messages to show the order.

PyTest

import pytest
import asyncio

@pytest.fixture
async def async_resource():
    print('Setup start')
    await asyncio.sleep(0.1)  # simulate async setup
    resource = 'resource ready'
    yield resource
    print('Teardown start')
    await asyncio.sleep(0.1)  # simulate async cleanup

@pytest.mark.asyncio
async def test_async_fixture(async_resource):
    print(f'Test received: {async_resource}')
    assert async_resource == 'resource ready'

Important Notes

Remember to mark async test functions with @pytest.mark.asyncio to run them properly.

Async fixtures allow you to prepare and clean up resources that need waiting without blocking.

Summary

Async fixtures use async def and yield to manage setup and cleanup.

They are useful when your tests need async resources or operations.

Mark async tests with @pytest.mark.asyncio to run them correctly.