[Question] Async test client

I’m developing an app that requires async setup and teardown during testing. For example, I insert data into a Redis database using aioredis. I’m using pytest-asyncio to mark async test functions.

The test client uses the synchronous requests API and an ASGI adapter to call the Starlette app. The setup I described above doesn’t work with the adapter because it doesn’t expect an event loop to be running.

I haven’t worked with asyncio prior to using Starlette so I may be missing something obvious but do you have any suggestions for how to deal with this? I thought about more explicitly managing the event loop during testing but this seemed a bit tedious.

Another option was an async test client. I had a look at aiohttp and if a custom Connector could be used in place of the ASGI requests adapter but I didn’t spend much time on it.

For now, I cobbled together an async test client that combines the request setup from requests.Session and starlette.testclient. _ASGIAdapter.

By the way, if there’s a better place to ask questions, please let me know 😄

[and-semakin]

I’ll just put links here for future strangers.

• https://github.com/florimondmanca/asgi-lifespan#usage (see usage example here)
• https://pypi.org/project/asgi-lifespan/

Also awesome explanation about the async test client: https://fastapi.tiangolo.com/advanced/async-tests/ (it’s about FastAPI but it still should be applicable to pure Starlette).

My example of async test client fixture:

# conftest.py
from asgi_lifespan import LifespanManager
from httpx import AsyncClient


@pytest.fixture()
async def client() -> Iterator[AsyncClient]:
    async with LifespanManager(app):
        async with AsyncClient(app=app, base_url="http://test") as ac:
            yield ac


# test_app.py
@pytest.mark.asyncio
async def test_endpoint(client: AsyncClient) -> None:
    response = await client.get("/")
    assert response.status_code == 200
    assert response.json() == {"message": "Tomato"}

[ryankask]

@mackeyja92 Here’s a gist: https://gist.github.com/ryankask/90c0dc155d3f95a52a1eaa0ac4ef63d0.

I needed to make it async all the way down to this call loop.run_until_complete(connection(receive, send)) deep in the adapter so a nested loop wasn’t started.

To do this, I combined the ASGI adapter Tom wrote with requests’ Session API. I removed some of the Session-related code that I didn’t think was relevant but I may have removed or left in too much.

I use pytest with pytest-asyncio doing something like this

@pytest.fixture
def client():
    return StarletteTestClient(starlette_app)

@pytest.mark.asyncio
async def test_update_company(client):
    company = await CompanyStore.create(name="Great Software")
    data = {
        "name": "Awesome Software",
    }

    response = await client.patch(f"/companies/{company.id}", json=data)

    assert response.status_code == 200
    updated_company = await CompanyStore.get(company.id)
    assert updated_company.name == "Awesome Software"

All my app code is async so to test in same way I’ve always done (arrange, act, assert, this time asynchronously), I think I need an async test client. This way pytest-asyncio can manage the loop and I can use pytest naturally. Maybe I need to just change the way I test so hopefully someone points out a better way.

I thought it would be better to use aiohttp’s equivalent of a requests’ adapter but I didn’t spend much time figuring it out.