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Graph/fastapi-test-validation-drift

AntiPattern

FastAPI Test Validation Drift

fastapi-test-validation-drift

A recurring validation mismatch where FastAPI dependency wiring and request parameter semantics differ between runtime and pytest setup, causing 422 Unprocessable Entity responses and missing/None query fields unless middleware/import timing and parameter declarations are aligned.

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Updated4/30/2026

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30 linked nodes

MATCHESSolution

parse.error.flatten().fieldErrors — Nextjs server action with zod validation. Tension: hard to return errors and show them in the UI. Outcome: form.setError(error.field, { message: error.message });.

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You should really use tag validation to trigger your query endpoints to refetch upon any successful mutation. — onSuccess: async () => { await queryClient.invalidateQueries({ queryKey: ["vehicle.getVehiclesWithMakes"],. Tension: Both are less than ideal. Outcome: await queryClient.invalidateQueries({ queryKey: ["vehicle.getVehiclesWithMakes"], // <-- invalidates tag key });.

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handle a scenario when the code is fine but backend went offline — prefetching data with usePrefetchQuery. Tension: prefetch works.

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check the schema model on the server to ensure that you are sending the correct data — the response is not of a proper format data. Tension: including the required fields like id. Outcome: you can define useMutation for get some correct error.

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Have you tried awaiting the API response? — If that doesn't work, try initializing the table with mock data. Tension: to see if that works. Outcome: awaiting the API response.

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We can fix this by giving a default response like this: — app/api/test/route.ts. Tension: No response is returned from route handler. Outcome: return NextResponse.json({data: "Uh oh! Resource Not Found"}, {status: 404}).

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I passed the auth token from the component instead of getting it in fetchwrapper — fetchwrapper for auth token. Tension: reason being I was getting the cookies in fetchwrapper for auth token. Outcome: solved my issue.

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Yes, it's Ok to use such decorators. — @review_router.get("/review") @admin_required async def get_review():. Tension: This use-case is covered by tests in FastAPI repo. Outcome: This use-case is covered by tests in FastAPI repo: https://github.com/fastapi/fastapi/blob/6513d4daa16a536d17743de6a292f49bd06388a4/tests/test_dependency_wrapped.py#L183-L200.

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There are a few things you can do. The first thing I would try is having a function which evaluates after import — the test setup will do the middleware patch. Tension: your function will return the correct value.

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If you convert all operations to perform asynchronously (using `aiosqlite`) , the issue will be mitigated. — When a route in FastAPI is listed as asynchronous (`async def`). Tension: that doesn't fully solve the inherent single writer problem of Sqlite. Outcome: Here's a fully operational update of the FastAPI server logic:.

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You can use `@model_serializer` to achieve this: — This will work as a FastAPI response model. Tension: but will still generate an unnested JSON schema in the OpenAPI documentation. Outcome: return {k: v for k, v in model_iter(self)}.

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This issue on github offers a solution github. — since fastapi and fastHTML are focusing on diffrent logics. Tension: there are diffrent tools included. Outcome: but since fastapi and fastHTML are focusing on diffrent logics.

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my temporary solution is to use 0.69.0 — upgrade of fastapi from 0.69.0 to 0.115.7. Tension: the true resolution to the question asked. Outcome: use 0.69.0.

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Move the initialization of `qdrant_client` into lifespan. Outcome: override using standard FastAPI mechanism.

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You can use a global dependency: — FastAPI. Tension: there's no way to set auth tokens in the docs. Outcome: app.openapi = custom_openapi.

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Could try adding catch_response to see what's actually happening. Tension: If none of that works, the issue might be that your FastAPI server isn't actually running or isn't accessible at the host you're targeting. Outcome: print(f"Status: {response.status_code}, Text: {response.text}").

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Try `fastapi run` instead of `fastapi dev` — if you use --reload or reload=True.

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This mismatch necessitates a manual conversion of the OpenAPI document to version 2.0 — before it can be utilized by API Gateway. Tension: Incompatibility issue between the OpenAPI document supported by GCP API Gateway, and the OpenAPI document automatically generated from FastAPI itself. Outcome: The Solution: For this will be clearly explained in the Link.

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use `pytest_asyncio` and the async fixture — If you don't want to utilize an `AsyncClient` like the one by `httpx`. Tension: ensuring that the FastAPI app's lifespan context correctly works.

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Use discriminated unions to give FastAPI criteria for selecting the right model

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Working Example. Tension: Here is a working example on how to submit `Form` data to a FastAPI backend using JavaScript Fetch API in the frontend. Outcome: body: formData.

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Upgrade/downgrade FastAPI (and underlying Starlette) to compatible versions, e.g., reinstall with a specific FastAPI version such as fastapi==0.115.6 after uninstalling fastapi/starlette/pydantic.

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Use this model for response validation — And you can do use Pydantic validation. Outcome: or use Depends() with Pydantic model.

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ASGIMiddleware. Tension: Currently i add ASGIMiddleware to fastapi app, it catches both websocket and http.

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I have solved it using the lifespan of FastAPI. — use it inside the routes. Tension: I couldn't identify where the problem is. Outcome: I have just initialized the Pubsub client in LifeSpan.

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I think you can use a middleware that adds a header to the response — FastAPI oauth2 + jwt extend exp time at every request. Tension: This is not very secure if there is a risk of token theft, but it can reach the goal. Outcome: response.headers["bearer-refreshed"] = access_token.

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making sure you pace your requests to stay below those limits — API rate limits. Tension: allowing room for your normal operations, too. Outcome: handle any 429 responses gracefully to retry.

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I have to pass it the full format of a "timestamp" — in the json we send in Postman/thunder. Tension: otherwise it will fail. Outcome: I found out what is wrong here.

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Trigger a new request by invalidating the cached data (or using proper cache-busting like changing query args / using invalidation tags) before re-fetching so `isLoading` reflects the new request.

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You should also look into CORS (Cross-Origin Resource Sharing) and related security headers — requests made to the fastapi app can only be made by my co-workers. Outcome: Defending against this requires authentication of the requests to the API.

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