Asyncio

Pytest · Reference cheat sheet

📋 Overview

pytest-asyncio runs async def tests and fixtures. Modern default is asyncio_mode = auto so marked or auto-detected coroutines work cleanly.

🔧 Core concepts

Piece	Role
`pytest.mark.asyncio`	Mark async test (strict mode)
`asyncio_mode`	`strict` \| `auto`
Async fixtures	`async def` + await setup
`event_loop`	Legacy loop fixture (avoid new code)
`AsyncMock`	Mock awaitables

Prefer one event loop policy per process; be careful with xdist.

💡 Examples

Install & config:

python -m pip install pytest-asyncio

[tool.pytest.ini_options]
asyncio_mode = "auto"
asyncio_default_fixture_loop_scope = "function"

Async test:

import pytest
import httpx

@pytest.mark.asyncio
async def test_ping():
    async with httpx.AsyncClient() as client:
        r = await client.get("https://example.com")
    assert r.status_code == 200

With asyncio_mode = auto, the mark is optional for async tests.

Async fixture:

@pytest.fixture
async def db_pool():
    pool = await create_pool()
    yield pool
    await pool.close()

async def test_row(db_pool):
    assert await db_pool.fetchval("SELECT 1") == 1

Mock async:

from unittest.mock import AsyncMock

async def test_service():
    fetch = AsyncMock(return_value={"id": 1})
    assert await fetch() == {"id": 1}

⚠️ Pitfalls

Mixing sync fixtures that block the loop heavily.
Forgetting await on coroutine mocks → always-true assertions.
Session-scoped async fixtures with function-scoped loops.
Sharing aiohttp/httpx clients across tests without reset.
Nested event loops (asyncio.run inside async tests).

Asyncio

Asyncio

📋 Overview

🔧 Core concepts

💡 Examples

⚠️ Pitfalls

🔗 Related

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