Jest React Testing

This is a solid reference for anyone writing tests with Jest and React Testing Library. It walks through Jest config for both JavaScript and TypeScript projects, covers the query priority system (getByRole first, getByTestId as last resort), and includes practical patterns for mocking, async testing, and custom hooks. The setup file examples are especially useful since they handle common gotchas like mocking matchMedia and IntersectionObserver. You'll want this when you're setting up a new React project's test infrastructure or when your team needs alignment on testing philosophy. It follows the "test behavior, not implementation" approach throughout, which saves you from brittle tests that break on refactors.