Backend & systems·Deployment, release and rollback
you send a copy of real production traffic at the new service and throw the responses away, just to see if it holds up.
Dark launch
Also calledshadow traffic, traffic mirroring
Exercising new code with real traffic while its output is discarded. It reveals load, latency and error behaviour under a realistic distribution that no synthetic test reproduces. Anything with side effects has to be stubbed, or you will double-charge somebody in the name of testing.