Testing in Production
Production is not a substitute for tests, but it is a place where hypotheses meet reality.
No test environment is a perfect copy of production. Data distribution, network latency, and the timing of background jobs all change the shape of a failure. Testing in production is not an excuse to skip the test suite; it is an acknowledgment that some risks only become visible when the system is doing real work.
The practical version is to make changes observable and reversible. Ship behind a flag, compare old and new behavior, and keep rollback boring. When an experiment fails, the goal is to learn quickly and keep the blast radius small, not to prove that the original plan was right.