FastAPI + pytest: RuntimeError: Event loop is closed when testing logout with AsyncClient

Question

I'm testing a FastAPI application with asynchronous endpoints using pytest and httpx.AsyncClient. I have an endpoint /logout that depends on a JWT token from cookies and uses some async dependencies.

Here is my test:

import pytest
from httpx import ASGITransport, AsyncClient
from unittest.mock import AsyncMock

from app.main import app 


@pytest.mark.asyncio
async def test_auth_callback_creates_user(monkeypatch):
    mock_user = AsyncMock()
    mock_user.id = 123

    async def mock_authorize_access_token(request):
        return {"userinfo": {"email": "[email protected]", "given_name": "Test", "sub": "xyz"}}

    monkeypatch.setattr("app.routers.view.core_views.google.authorize_access_token", mock_authorize_access_token)
    monkeypatch.setattr("app.routers.view.core_views.get_user_email", AsyncMock(return_value=None))
    monkeypatch.setattr("app.routers.view.core_views.add_user", AsyncMock(return_value=mock_user))
    monkeypatch.setattr("app.routers.view.core_views.encode_jwt", lambda payload: "fake-jwt")
    monkeypatch.setattr("app.routers.view.core_views.save_jwt_token", AsyncMock())

    async with AsyncClient(
        transport=ASGITransport(app=app),
        base_url="http://test"
    ) as ac:
        resp = await ac.get("/auth/callback")

    assert resp.status_code == 302
    assert resp.headers["location"] == "/profile-view/"
    assert "access_token" in resp.cookies


@pytest.mark.asyncio
async def test_user_fixture(monkeypatch):
    mock_user = AsyncMock()
    mock_user.id = 123
    assert mock_user.id is not None


@pytest.mark.asyncio
async def test_logout_removes_cookie(monkeypatch):
    mock_payload = {"sub": "1"}
    monkeypatch.setattr("app.routers.view.core_views.get_current_token_payload", AsyncMock(return_value=mock_payload))
    monkeypatch.setattr("app.routers.view.core_views.blacklist_token", AsyncMock())

    async with AsyncClient(
        transport=ASGITransport(app=app),
        base_url="http://test"
    ) as ac:
        resp = await ac.get("/logout", cookies={"access_token": "fake-token"})

    assert resp.status_code == 302
    assert resp.headers["location"] == "/authentication"

command: poetry run pytest -v tests/test_user_oauth.py

requirements.txt: (necessary)

fastapi==0.112.4
httpx==0.28.1
pytest==8.3.4
pytest-asyncio==1.0.0
pytest-mock==3.14.1
SQLAlchemy==2.0.36
asyncpg==0.30.0
alembic==1.14.0
Authlib==1.4.0
python-dotenv==1.0.1
redis==6.2.0
PyJWT==2.10.1

I want to test that /logout returns a 302 redirect and removes the cookie. But instead I get an error. FAILED tests/test_user_oauth.py::test_logout_removes_cookie - RuntimeError: Event loop is closed

What I've tried:

Putting the ASGITransport into pytest fixtures
Explicitly closing the client with await ac.aclose() at the end of the test.
Switching pytest.mark.asyncio to pytest.mark.anyio with anyio_backend = asyncio.
looked at other posts on this topic.

This question is similar to: How do you use httpx AsyncClient with pytest in fastapi?. If you believe it’s different, please edit the question, make it clear how it’s different and/or how the answers on that question are not helpful for your problem. — dimakin
– dimakin, Commented Oct 7 at 17:19

onesch · Accepted Answer · 2025-10-07 21:07:44Z

1

The problem was caused by the event loop being closed between async tests. pytest-asyncio creates and destroys an event loop per test by default (scope = function).

That’s why I was getting:

RuntimeError: Event loop is closed

I fixed it by extending the event loop lifetime with:

@pytest.mark.asyncio(loop_scope="session")

Example:

@pytest.mark.asyncio(loop_scope="session")  # keeps one event loop for all async tests
async def test_eat_cookie():
    ...
# other async tests

Result: All tests passed, no more RuntimeError: Event loop is closed.

answered Oct 7 at 21:07

onesch

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