Testing Your Web App: Unit, Integration, and E2E Tests

Testing isn't about achieving 100% coverage—it's about building confidence in your code. A balanced testing strategy uses multiple levels. Unit tests verify individual functions or components in isolation. Jest and Vitest are popular for JavaScript, testing pure logic without external dependencies. They're fast and catch low-level regressions early. Integration tests check how multiple units work together. Testing React components with React Testing Library focuses on user interactions rather than implementation details. You test that a button click updates the UI, not which internal state variable changed. This approach produces more resilient tests. End-to-end (E2E) tests simulate real user scenarios across your entire application. Playwright and Cypress have made E2E testing dramatically easier—they run actual browsers, can take screenshots, and provide excellent debugging tools. The testing pyramid suggests many unit tests, fewer integration tests, and even fewer E2E tests. Start by testing critical user paths: user registration, checkout flows, and core functionality. Automate tests in your CI/CD pipeline to catch issues before they reach production. The initial investment pays off in reduced debugging time and confidence to refactor and add features.