Writing tests for the ASGI lifespan protocol with HTTPX

This post is over three years old. Some of it may no longer reflect current tooling or my current view.

Uvicorn silently ignores exceptions that occur during startup against the ASGI lifespan protocol - see starlette/issues/486.

You can disable this feature using the lifespan="on" parameter to uvicorn.run() - which Datasette now does as-of 16f592247a2a0e140ada487e9972645406dcae69

This exposed a bug in datasette-debug-asgi: it wasn’t handling lifespan events correctly. datasette-debug-asgi/issues/1

The unit tests weren’t catching this because using HTTPX to make test requests doesn’t trigger lifespan events.

Florimond Manca had run into this problem too, and built asgi-lifespan to address it.

You can wrap an ASGI app in async with LifespanManager(app): and the correct lifespan events will be fired by that with block.

Here’s how to use it to trigger lifespan events in a test:

from asgi_lifespan import LifespanManager

@pytest.mark.asyncio
async def test_datasette_debug_asgi():
    ds = Datasette([], memory=True)
    app = ds.app()
    async with LifespanManager(app):
        async with httpx.AsyncClient(app=app) as client:
            response = await client.get("http://localhost/-/asgi-scope")
            assert 200 == response.status_code
            assert "text/plain; charset=UTF-8" == response.headers["content-type"]

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