End-to-end tests run the application in a browser-like environment and validate complete workflows. They are valuable for login, checkout, critical forms, routing, permissions, and other journeys where multiple systems must work together.

Because E2E tests are slower and more environment-sensitive, keep them focused. Use deterministic test data and isolate external dependencies where necessary.

A failing E2E test should make it easy to determine whether the problem is UI, API, authentication, data, or infrastructure.