What is end-to-end testing?

End-to-end (E2E) testing validates a complete user journey through the real stack - UI, APIs, auth, databases, and integrations - not isolated units in isolation. A typical E2E case might sign up, configure an account, perform a core action, and confirm the outcome visible to the user. It catches wiring problems that unit and integration tests miss, such as broken redirects, wrong environment config, or third-party widget failures. E2E runs are slower and need stable test data and environments, so teams automate the most critical paths rather than every edge case. E2E sits at the top of the test pyramid: fewer tests, higher confidence on production-like flows. It works best alongside faster tests below it, not as the only safety net.