How an API fails is part of its contract too. These tests describe the behavior you'd demand from a production API. You'll keep them in their own Unhappy Path folder, so your suite cleanly separates the requests that should succeed from the ones that should fail.
Confirm a Missing Resource Returns 404
Ask for a movie that doesn't exist and a well-behaved API returns 404 — a clear, catchable signal. A broken one returns 200 with null, or a 500, forcing every client into defensive guesswork. A negative test makes "fails predictably" a requirement.
In Agent Mode, run a prompt like:
In my Movies API collection, create a folder named "Unhappy Path" at the collection root. Then add a new request as a child of that "Unhappy Path" folder — not at the collection root — named "GET /movies/animation/999999", and give it a post-response test that asserts the status code is 404 for a movie id that does not exist.
Check the placement: Agent Mode sometimes creates the folder but drops the request beside it instead of inside it. Confirm "GET /movies/animation/999999" is nested under Unhappy Path in the collection sidebar — if it isn't, drag it in, or ask Agent Mode to "move the 999999 request into the Unhappy Path folder."
The Movies API sandbox may return 200 with an empty body instead of 404 — in which case this test fails, and that failure is the test doing its job. It documents exactly how this API differs from the ideal.
See it for yourself: Send the GET /movies/animation/999999 request and open the Test Results tab. Against this sandbox the 404 test will likely show a red FAIL (it returns 200 with an empty body) — that failure is the test documenting how this API differs from the ideal.
Send Invalid Input to a Write Endpoint
If you POST a movie with no title, the API should reject it with a 4xx and a useful message — not accept it silently, and never 500. Testing validation guarantees bad data gets stopped at the door instead of corrupting everything downstream.
In Agent Mode, run a prompt like:
Duplicate the POST request and place the copy as a child of the "Unhappy Path" folder — not at the collection root — named "POST /movies/animation (invalid)", with a body missing the required title field. Add a post-response test asserting the status code is in the 400–499 range and is not a 500 server error.
Check the placement: Confirm the invalid POST is nested under Unhappy Path alongside your 404 request. If it landed at the collection root, drag it into the folder or ask Agent Mode to move it there.
The sandbox doesn't enforce a schema, so it will likely accept the invalid body and this test will fail. Keep it anyway — it encodes the behavior you'd demand from production and turns green the moment you run the suite against a real API.
See it for yourself: Send the invalid POST and open the Test Results tab — the 4xx test will likely show a red FAIL against the sandbox. That's expected; keep it, and it turns green the moment you run against a real API.