Concurrency Testing
Concurrency testing checks whether a system behaves correctly when multiple processes, threads, or users access shared resources at the same time — looking for race conditions, deadlocks, and data corruption that only appear under simultaneous access. Bugs here are notoriously intermittent and hard to reproduce on demand.
A classic concurrency bug: two users update the same record at nearly the same instant, and depending on exact timing, one update silently overwrites the other instead of both being applied or one being rejected. The bug might occur once in a thousand attempts, making it almost useless to test for by just clicking around manually.
Effective concurrency testing usually needs deliberately engineered scenarios — scripted simultaneous requests, thread-sanitizing tools, or stress and load tests that push enough real concurrent traffic to surface timing-dependent bugs that a single-user test session would never hit.
