CtrlK
BlogDocsLog inGet started
Tessl Logo

testland/pytest-asyncio-patterns

Configures and runs async Python tests with pytest-asyncio: installs the plugin, selects asyncio_mode (auto vs strict), scopes event loops (function/class/module/session), writes async fixtures with @pytest_asyncio.fixture, mocks coroutines with AsyncMock, and tests FastAPI (httpx.AsyncClient + ASGITransport) and aiohttp (aiohttp_client fixture) applications. Use when a Python project contains async def test_ functions, FastAPI/aiohttp endpoints, or any asyncio-based code that needs pytest integration. Do NOT use for general pytest fixture design, parametrize patterns, or conftest.py structure without an asyncio-specific problem (event-loop scoping, mode config, AsyncMock, ASGI client): use python-unit-tests for those.

93

Quality

93%

Does it follow best practices?

Impact

—

Average score across 10 eval scenarios

SecuritybySnyk

Passed

No findings from the security scan

Overview
Quality
Evals
Security
Files

framework-clients.mdreferences/

Async framework client patterns

Deeper framework-specific async test patterns. The SKILL.md spine keeps the minimal FastAPI AsyncClient example; FastAPI lifespan events, aiohttp, and anyio live here.

FastAPI lifespan events (asgi-lifespan)

AsyncClient does not fire lifespan events by default (per fastapi.tiangolo.com/advanced/async-tests). To trigger startup/shutdown handlers, use asgi-lifespan:

pip install asgi-lifespan
from asgi_lifespan import LifespanManager

@pytest_asyncio.fixture(scope="module")
async def live_app():
    async with LifespanManager(app) as manager:
        yield manager.app

@pytest.mark.asyncio(loop_scope="module")
async def test_with_lifespan(live_app):
    async with AsyncClient(
        transport=ASGITransport(app=live_app),
        base_url="http://test",
    ) as client:
        response = await client.get("/health")
    assert response.status_code == 200

aiohttp apps (pytest-aiohttp)

Per docs.aiohttp.org/testing, the pytest-aiohttp plugin provides an aiohttp_client fixture that manages server startup and teardown:

pip install pytest-aiohttp
# pyproject.toml
[tool.pytest.ini_options]
asyncio_mode = "auto"
from aiohttp import web

async def hello(request):
    return web.Response(text="Hello, world")

async def test_hello(aiohttp_client):
    app = web.Application()
    app.router.add_get("/", hello)
    client = await aiohttp_client(app)
    resp = await client.get("/")
    assert resp.status == 200
    text = await resp.text()
    assert text == "Hello, world"

aiohttp_client returns a TestClient that starts the server on a random port and shuts it down after the test.

anyio as an alternative

Per anyio.readthedocs.io/testing, anyio ships its own pytest plugin that runs async tests on both asyncio and Trio backends. Use it when the codebase is written against anyio primitives or when multi-backend verification is needed.

pip install anyio[trio]
import pytest

@pytest.mark.anyio
async def test_anyio_style():
    result = await compute()
    assert result == 42

Parametrize backends:

# conftest.py
import pytest

@pytest.fixture(params=["asyncio", "trio"])
def anyio_backend(request):
    return request.param

anyio conflicts with pytest-asyncio auto mode; when both plugins are present, set only one to auto.

references

asyncmock-assertions.md

framework-clients.md

SKILL.md

tile.json