starlette: pytest event loop is already running

Because the test client calls loop.run_until_complete(connection(receive, send)), I cannot use anything that modifies the event loop in a pytest fixture without getting RuntimeError: This event loop is already running.

I would like to use a package like aresponses to mock aiohttp requests like this:

@pytest.fixture
def mock_endpoint(aresponses):
    aresponses.add('mock.com', '/test/', 'get', 'this is my mock response')

After messing with it for a couple hours, the only way I was able to get successful tests was to wrap the application in middleware:

@pytest.fixture
def app():
    class App:
        def __init__(self, app):
            self.app = app

        def __call__(self, scope):
            return functools.partial(self.asgi, scope=scope)

        async def asgi(self, receive, send, scope):
            async with ResponsesMockServer() as aresponses:
                aresponses.add('mock.com', '/test/', 'get', 'this is my mock response')
                inner = self.app(scope)
                await inner(receive, send)
    return App(application)


@pytest.fixture
def test_client(app):
    with TestClient(app) as test_client:
        yield test_client

I am going to modify this to allow myself to dynamically pass responses through the @pytest.mark decorator, but this workflow is not really convenient at all.

Am I missing something here? Is there a better way to set up my test clients, or should I just keep going down this route?

Thanks

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About this issue

Original URL
State: closed
Created 5 years ago
Reactions: 6
Comments: 23 (8 by maintainers)

Commits related to this issue

Draft for the async test client (#440) — committed to gvbgduh/starlette by gbgduh 5 years ago

Most upvoted comments

Just FYI, I’m also stumbling over this currently trying to use the TestClient in an async test function (with pytest-asyncio). Minimal test case:

import pytest
from starlette.responses import HTMLResponse
from starlette.testclient import TestClient

async def app(scope, receive, send):
    assert scope['type'] == 'http'
    response = HTMLResponse('<html><body>Hello, world!</body></html>')
    await response(scope, receive, send)

@pytest.mark.asyncio
async def test_app():
    client = TestClient(app)
    response = client.get('/')
    assert response.status_code == 200

Fails with “RuntimeError: This event loop is already running” too. I guess there is currently no workaround, aside from just not using async tests, which I think wouldn’t work in my specific case.

Thank you for working on this!

+13

teskje on Jun 27, 2019

I have a similar problem where I’m also trying to embed a database connection with a transaction active for the current test in the request.state. I haven’t quite found the magic configuration of pytest, pytest-asyncio, and TestClient to make this work yet.

Basically, I’d love to see an example of how to use TestClient along with databases/asyncpg.

taybin on Sep 12, 2019

@taybin - I just found this library, after much wailing and gnashing of teeth with errors like the one in this issue. It worked for me; hope it helps you, too.

EDIT: Just realized I responded in a different issue than I meant to about a similar problem, but I’ll leave it in case it’s helpful.

tomplex on Sep 12, 2019

Found a workaround from some other issue.

import nest_asyncio
nest_asyncio.apply()

at the top of the code.

eddebc on Aug 25, 2019

Did anyone found a solution that doesn’t involve hacking (without nesting loops)?

I only use the httpx-based client as described in https://github.com/encode/starlette/issues/652#issuecomment-569327566 and it works very well. Together with asgi-lifespan, also startup and shutdown tasks are executed: https://github.com/florimondmanca/asgi-lifespan

chbndrhnns on Aug 9, 2022

I used the starlette TestClient with nest_asyncio as a workaround for this problem, but I changed to use async-asgi-testclient. It works very well so far.

otsuka on Jan 14, 2020

@dmontagu Hey, this library is on MIT license now 😃

adsko on Dec 10, 2019

I had a similar problem running pytest and the ASGI server in the same event loop and found this solution don’t know if it’s useful for you. Still gives some warning about files still open when closing the server

jacopofar on Aug 26, 2019

Okay - that’s kinda awkward.

It’s a bit of a side effect of the fact that the existing TestClient exposes a sync interface. See also https://github.com/encode/databases/issues/32#issuecomment-465728135

Given that I’ve just released this… https://github.com/encode/requests-async one thing we could look at doing would be moving to having an async test client (requests-async, but with an ASGI adapter) and using async test cases. (pytest-asyncio seems to have that covered.)

tomchristie on Mar 21, 2019