Frontend Testing Best Practices

This is a testing strategy that pushes you toward end-to-end tests and away from component unit tests. It's opinionated: default to E2E, only unit test pure functions, minimize mocking, and test user behavior instead of React component internals. The rules cover selector preferences (role over CSS), test structure (E2E tests go in e2e/tests/, unit tests colocate with source), and when to bail on mocks and write an E2E test instead. If you've been maintaining a sprawling component test suite that breaks on every refactor, this gives you permission to delete most of it. The tradeoff is you need a solid E2E setup, which means Playwright or similar actually working in your project.