Sample

Test a FastAPI app with TestClient and no network, and assert the validation error bodies it returns

sha256:8bcaa6f98cea6edf681d2b0f76a18856106de62aab70009b1d22a5a50abb1257

Case

Goal

Test a FastAPI app with TestClient and no network, and assert the validation error bodies it returns HOW

Packages

fastapi 0.141.1 starlette 1.6.0 httpx2 2.10.0 httpx 0.28.1 pydantic 2.13.4

Environment

python 3.12

Created

2026-08-14T08:53:22Z

Contract

• assert TestClient targets http://testserver, so the run needs no socket, no port and no DNS
• assert TestClient drives the real ASGI pipeline, so pure ASGI middleware runs and stamps a header on the response
• assert calling the endpoint function directly does no coercion, so it returns nonsense instead of a 422
• assert an int path parameter given text answers 422 with detail[0].type int_parsing and loc path/item_id
• assert every 422 entry carries exactly type, loc, msg and input, and input echoes the submitted body back to the caller
• assert a missing body field answers 422 with type missing and loc body/age
• assert a valid body answers the declared 201 and response_model removes the extra field the handler returned
• assert an unexpected field in the request body is ignored by the model rather than rejected
• assert HTTPException(404) serialises to a single detail string
• assert the lifespan runs only when TestClient is entered as a context manager, so a plain client leaves startup unrun
• assert starlette 1.6 binds httpx2 for TestClient when both httpx2 and httpx are installed, so the response is not an httpx.Response
• assert raise_for_status on a TestClient response raises httpx2.HTTPStatusError, which except httpx.HTTPStatusError does not catch
• assert fastapi.testclient.TestClient is starlette's class re-exported unchanged
• assert hiding httpx2 makes the import fall back to httpx with a StarletteDeprecationWarning, which is a UserWarning and not a DeprecationWarning

Files

• csx.json
• requirements.txt
• src/__init__.py
• src/app.py
• test/contract.py

Origin Seeder

anonymous

Verification receipts

• python 3.12 · CONTAINER_RUN · compile:SKIPPED · contract:PASS · load:PASS · resolve:PASS · python@1 · 2026-08-14 · ed25519:a2ec939a4c60e243
• · CONTAINER_RUN · compile:SKIPPED · contract:FAIL · load:SKIPPED · resolve:PASS · python@1 · 2026-08-14 · ed25519:7da3f610facce8bf