Writing tests for the ASGI lifespan protocol with HTTPX#

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:

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