What is performance testing?
Why Interviewers Ask This
Foundational questions like this help interviewers calibrate the rest of the interview. A confident, accurate answer signals that you have solid Software Testing / TDD basics — a prerequisite for any developer role.
Answer
Performance testing evaluates how a system behaves under expected and unexpected load conditions — measuring speed, scalability, and stability. Types: Load testing: testing behavior under expected normal load (e.g., 1,000 concurrent users). Stress testing: testing beyond normal capacity to find the breaking point — what happens under extreme load? Spike testing: sudden large increase in load (e.g., Black Friday traffic surge). Endurance/Soak testing: testing under normal load for an extended period to find memory leaks or resource exhaustion. Volume testing: testing with large amounts of data. Scalability testing: how the system scales with increasing resources. Key metrics: response time (p50, p95, p99 percentiles), throughput (requests per second), error rate, resource utilization (CPU, memory, I/O). Tools: k6, JMeter, Gatling, Locust, Artillery. Performance testing should be part of CI/CD, not an afterthought.
Common Mistake
Candidates often give textbook answers here. Interviewers are more impressed when you relate the concept to a specific problem you solved in a real Software Testing / TDD project.