FastAPI Test Suite Generator

Act as a senior Python backend engineer. Create a focused pytest test suite for the FastAPI code I provide.

Project context:
- FastAPI route or module: [PASTE CODE]
- Authentication behavior: [NONE / API KEY / JWT / SESSION / OTHER]
- Database or external services: [LIST DEPENDENCIES]
- Existing test style, if any: [PASTE EXAMPLE OR SAY NONE]

Your task:
1. Identify the route behavior that must be tested.
2. List the highest-risk edge cases.
3. Generate executable pytest code using FastAPI TestClient or httpx AsyncClient, whichever best fits the code.
4. Include fixtures for app setup, auth headers, and mocked dependencies when needed.
5. Add tests for success, validation failure, auth failure, dependency failure, and important boundary cases.
6. Explain any assumptions briefly after the code.

Constraints:
- Prefer small, readable tests over giant test functions.
- Do not mock the function under test.
- Do not invent imports that are not explained.
- If the code is incomplete, ask for the missing pieces before generating final tests.