Green Tests Can Hide Architecture Bottlenecks in Distributed Systems

A developer building a claims-processing pipeline discovered that passing all integration and end-to-end tests did not guarantee the system would perform well under real-world load. When load testing was introduced, KEDA autoscaling added more worker pods, but throughput became erratic as competing workers contended for the same provider-level locks. The correctness mechanism designed to prevent race conditions inadvertently became the bottleneck limiting scalability. No existing test had simulated dozens of workers competing for shared resources, revealing that correctness and throughput are distinct system qualities. The key takeaway is that a green test suite validates code logic, but only realistic load testing can expose whether the underlying architecture holds up under concurrency.