FastAPI "RuntimeError: There is no current event loop" in CI

An async test or fixture called asyncio.get_event_loop() when no loop was running. On recent Python versions that no longer auto-creates a loop, and without pytest-asyncio driving the test, the coroutine has nothing to run on.

What this error means

An async FastAPI test fails with "RuntimeError: There is no current event loop in thread 'MainThread'" or a coroutine "was never awaited" warning and no assertions run.

RuntimeError: There is no current event loop in thread 'MainThread'.

  loop = asyncio.get_event_loop()

Common causes

pytest-asyncio is not driving the async test

Without pytest-asyncio (and its mode), an async def test is collected but never awaited, so loop-dependent code fails.

get_event_loop with no running loop on newer Python

Recent Python deprecated auto-creating a loop in get_event_loop(), so code that assumed one exists now raises.

How to fix it

Install and enable pytest-asyncio

1. Install pytest-asyncio in the test environment.
2. Set an asyncio mode so async tests are awaited.
3. Use an async client such as httpx.AsyncClient with the app.

import pytest, httpx
from app.main import app

@pytest.mark.asyncio
async def test_health():
    transport = httpx.ASGITransport(app=app)
    async with httpx.AsyncClient(transport=transport, base_url="http://test") as ac:
        r = await ac.get("/health")
    assert r.status_code == 200

Get the running loop instead of a current one

Inside async code, use asyncio.get_running_loop() rather than get_event_loop().

import asyncio
loop = asyncio.get_running_loop()

How to prevent it

• Drive async tests with pytest-asyncio and an explicit mode.
• Use get_running_loop() inside coroutines.
• Prefer async clients for async endpoints instead of manual loops.

Related guides