Most software failures now stem from service interactions, not isolated code bugs. Teams struggle balancing integration, end-to-end (E2E), and system tests. Misuse slows pipelines and undermines confidence.

Integration tests offer the best ROI for backend systems. They verify API communications, database interactions, and message flows faster than E2E tests. Real teams use them extensively in PR pipelines for quick feedback.

E2E tests should focus on critical user paths like sign-up or checkout. Running them excessively in CI causes delays. System tests are reserved for pre-release validation, ensuring release readiness under real-world conditions.

Smart CI setups run unit and integration tests on every PR, smoke-level E2E tests post-merge, and full system tests overnight. Teams that flip this pyramid risk flaky builds and slow delivery cycles.