API Rate Limit Testing
API rate limit testing verifies that a system correctly enforces its request-throttling rules — rejecting or delaying requests once a client exceeds its allowed rate — and that legitimate traffic under the limit is never incorrectly blocked. Both failure directions matter: too permissive invites abuse, too strict breaks real users.
Testing typically confirms the exact threshold behavior: requests at or under the limit succeed, the request that crosses the threshold is correctly rejected (usually with a 429 status), and the limit resets on the documented schedule — sliding window, fixed window, or token bucket, depending on the algorithm in use.
Rate limits interact with concurrency in ways that are easy to get subtly wrong, so testing needs genuinely concurrent requests, not just sequential ones — a limiter that works correctly against requests sent one at a time can still have race conditions that only appear under real simultaneous load.
