React Testing Comprehensive React testing patterns for behavior-focused component tests, custom hook tests, accessibility assertions, and network-level mocking. When to Activate - Writing tests for React components, custom hooks, or pages - Adding test coverage to legacy untested components - Migrating from Enzyme or class-component-era patterns to React Testing Library - Setting up Vitest or Jest for a new React project - Mocking HTTP requests in tests - Asserting accessibility violations - Deciding which tests belong in RTL vs Playwright Component Testing vs full E2E Core Principle Test wha…