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nextjs-testing

Testing & Quality
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Write Jest or Vitest unit tests with React Testing Library and Playwright E2E tests for Next.js projects. Use when testing components with RTL, mocking APIs with MSW, or creating Playwright user flow tests.

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Next.js Testing

Priority: P1 (HIGH)

Test Runner

  • Existing projects (Pages Router / legacy stack): Use Jest (jest@29 + babel-jest + jest-environment-jsdom).
  • New projects (App Router): Use Vitest for speed and native ESM support.

Workflow: Test New Feature

  1. Write unit tests — Use Jest (or Vitest for new projects) + RTL with Arrange-Act-Assert pattern.
  2. Mock APIs — Set up MSW handlers for all fetch boundaries.
  3. Test interactions — Use userEvent (async) for clicks, typing, form submissions.
  4. Add E2E tests — Use Playwright for critical user flows (login, checkout).
  5. Verify coverage — Aim for 80%+ on core libraries via JSON coverage reports.

Component Test Example

See implementation examples

Implementation Guidelines

  • Unit Testing: Use Jest (existing projects) or Vitest (new projects) with React Testing Library (RTL). Follow Arrange-Act-Assert (AAA) patterns.
  • E2E Testing: Use Playwright for full user flow validation. Focus on critical flows (Login, Checkout).
  • Networking: Mock all internal/external API boundaries using Mock Service Worker (MSW). Ensure server and browser handlers correctly configured.
  • Interactions: Use userEvent (async) to simulate user actions: await user.click(button).
  • Selectors: Favor getByRole / findByRole to test accessibility. Use data-testid only as fallback.
  • Environment: For Jest, use jest-environment-jsdom. For Vitest, configure vitest.config.ts with jsdom or happy-dom.
  • Reporting: Ensure tests generate JSON coverage reports for CI gates. Aim for 80%+ coverage on core libraries.

Anti-Patterns

  • No real network usage in tests: Always use MSW handlers or mocks.
  • No implementation testing: Test user behavior, not internal methods.
  • No heavy E2E for unit logic: Use Jest/Vitest for isolated logic tests.
  • No global state leakage: Reset MSW handlers and mocks after each test.

References