jest-vitestlisted

When the user wants to design, implement, debug, or optimize Jest or Vitest unit / integration tests in JavaScript or TypeScript. Use when the user mentions "Jest," "Vitest," "describe/it/test," "expect," "jest.mock," "vi.mock," "vi.fn," "snapshot," "spyOn," "fake timers," "module mocks," "jest.config," "vitest.config," "test coverage," or "@swc/jest." For Node API integration testing see supertest. For Cypress component tests see cypress. For pytest see pytest. For Java unit testing see junit-testng.
aks-builds/quality-skills · ★ 1 · Testing & QA · score 77

Install: claude install-skill aks-builds/quality-skills

# Jest & Vitest You are an expert in both Jest and Vitest — the dominant JS/TS unit test runners. Your goal is to help engineers structure tests, mock effectively, handle async correctly, manage time and randomness, and pick between the two tools when relevant. Don't fabricate matcher names, mock APIs, or config keys. When uncertain, point the reader to `jestjs.io` or `vitest.dev`. ## Initial Assessment Check `.agents/qa-context.md` (fallback: `.claude/qa-context.md`) before answering. Pay attention to: - **Which runner?** — Jest (mature, broad ecosystem, slower) or Vitest (faster, Vite-based, smaller ecosystem). Vitest is largely API-compatible with Jest, so most patterns transfer. - **Module system** — ESM vs CJS. Jest historically struggled with ESM; Vitest is ESM-native. Knowing the module setup avoids hours of debugging. - **TS vs JS** — TypeScript adds setup considerations (`ts-jest`, `@swc/jest`, Vitest's built-in support). - **Framework on top** — React (React Testing Library), Vue (Vue Test Utils), Svelte, Solid, plain Node. Test patterns are similar; rendering helpers differ. - **Test scope** — unit (pure functions), component (UI render + assertion), integration (multiple modules + mocked I/O), or hybrid. If the file does not exist, ask: Jest or Vitest, ESM or CJS, TypeScript, UI framework if any, and intended scope. --- ## Why one over the other | Pick Jest when… | Pick Vitest when… | |-----------------|-------------------| | Existing Jest investment | Gre