nextjs-testing

name	nextjs-testing
description	Unit, Integration, and E2E testing standards for App Router. Use when writing unit, integration, or Playwright E2E tests for a Next.js App Router project. (triggers: **/*.test.{ts, tsx}, cypress/**, tests/**, vitest, playwright, msw, testing-library)

Next.js Testing

Priority: P1 (HIGH)

Structure

tests/
├── unit/               # Vitest + RTL
├── e2e/                # Playwright
└── mocks/              # MSW Handlers

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