Dependency Injection for startup in test client

[scottherlihy]

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Example Code

# currently:

@app.on_event("startup")
async def startup():
    load_defaults()
    await DB.start_db(settings=settings)
    return

# what I'd like
@app.on_event("startup")
async def startup(defaults_retriever=None):
    if not defaults_retriever:
        defaults_retriever = RealRetriever()
    load_defaults(defaults_retriever)
    await DB.start_db(settings=settings)
    return



# and then in tests I wouldnt need to mock the remote because I can do something like 
client = TestClient(app, startup_args=[MockDefaultsRetriever])

Description

Is it possible to pass an argument to the startup function of the TestClient?

https://fastapi.tiangolo.com/advanced/testing-events/

The docs suggest using TestClient to ensure the startup function gets invoked, but what if the startup function has an argument that is a class that hits a remote and Id like to mock it. Since patching module can be finicky dependency injection is a clean way to accomplish the goal of mocking an object and if something like I suggested in the example code was implemented it would make this very easy.

Operating System

macOS

Operating System Details

No response

FastAPI Version

0.70.0

Python Version

Python 3.9.7

Additional Context

No response

[DavidBord]

I think that if that would have been made possible then all the startup & shutdown events would have gotten these args. I wouldn't have used this feature if it was available.
Would you consider using partial from functools for your use case?

[a-n-d-i]

Hi, maybe just mock/patch RealRetriever? Or call the decorator directly? I mean you're already passing an Argument to Testclient, namely app. The startup stuff is just buried in there. So doing such an Argument list would be like passing the same stuff twice to avoid changing the insides of the app parameter.

[adriangb]

I think this duplicates the feature request in #617

[scottherlihy]

I agree, @adriangb. Closing.