RuntimeError during unit tests: Future attached to a different loop

[prashantgupta24]

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Example Code

from httpx import AsyncClient
from fastapi import FastAPI
from sse_starlette.sse import EventSourceResponse
import asyncio

app = FastAPI()

@app.post("/foo")
async def http_foo() -> EventSourceResponse:
    async def event_generator():
        yield {"data": "1"}
        yield {"data": "2"}
        yield {"data": "3"}
    return EventSourceResponse(event_generator())

def parse_event_stream(text):
    events = []
    for line in text.strip().split("\r\n\r\n"):
        events.append(line[len("data:"):].strip())
    return events

async def test_first():
    client = AsyncClient(app=app, base_url="http://test")
    async with client:
        response = await client.post("/foo")
    events = parse_event_stream(response.text)
    assert events == ["1", "2", "3"]

async def test_second():
    client = AsyncClient(app=app, base_url="http://test")
    async with client:
        response = await client.post("/foo")
    events = parse_event_stream(response.text)
    assert events == ["1", "2", "3"]

Description

Quoting from here: sysid/sse-starlette#68. Asking question here since no response in sse_starlette:

I tried to write pytest testcases for a FastAPI route that returns an event source/stream. The first test always succeedes, but the second test, despite identical content, consistently runs into an error: RuntimeError: Task ... got Future ... attached to a different loop. I'm not sure if the error is related to sse_starlette, fastapi, httpx or pytest-asyncio.

Operating System

macOS

Operating System Details

No response

FastAPI Version

0.104.0

Pydantic Version

2.4.2

Python Version

3.9.2

Additional Context

No response