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Jest / Vitest

Jest and Vitest are the dominant unit testing frameworks for JavaScript and TypeScript. Jest is the battle-tested choice bundled with Create React App and widely adopted across Node.js ecosystems. Vitest is the modern successor - it reuses Vite's transform pipeline, offers a compatible API, and is significantly faster for projects already on Vite. Both share the same describe/it/expect vocabulary, making knowledge transferable. This skill covers writing well-structured tests, mocking strategies, async patterns, snapshot testing, React component testing, and coverage analysis.

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