Next.js Testing

Priority: P1 (HIGH)

Workflow: Test a New Feature

1. Write unit tests — Use Vitest + 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

Structure

See implementation examples

Implementation Guidelines

• Unit Testing: Use Vitest for speed and React Testing Library (RTL) for component behavior. Follow Arrange-Act-Assert (AAA) patterns.
• E2E Testing: Use Playwright for full-stack App Router validation. Focus on User Flows (e.g., Login, Checkout).
• Networking: Mock all internal/external API boundaries using Mock Service Worker (MSW). Ensure server and browser handlers are correctly configured.
• RSC Testing: Test React Server Components (RSC) using the same patterns as libraries (SSR-compatible tests). Prefer E2E tests for complex async data-fetching logic.
• Interactions: Use userEvent (async) to simulate user actions: await user.click(button).
• Selectors: Favor getByRole / findByRole to test accessibility. Use data-testid only as a fallback.
• Environment: Configure vitest.config.ts with jsdom or happy-dom for component tests.
• 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 Vitest for isolated logic tests.
• No global state leakage: Reset MSW handlers and mocks after each test.

References

• Next.js Test Patterns