testing

Configure Vitest with the jsdom environment, a setup file registering @testing-library/jest-dom, and cleanup after each test. Add the React plugin and path aliases in vitest.config.ts, then write tests using render, screen, and fireEvent.

Use Testcontainers to spin up a real Postgres instance in tests, point Prisma at the mapped port, and run migrations before the suite. Clean tables with deleteMany in beforeEach to keep tests isolated.

Vitest handles unit, component, and integration tests with fast in-process execution, while Playwright runs E2E tests in real browsers across Chromium, Firefox, and WebKit. Follow the test pyramid: mostly Vitest, a small set of Playwright journeys.

Use MSW to intercept HTTP requests at the network layer with a setupServer instance defining route handlers. Start the server in beforeAll, reset handlers after each test, and error on unhandled requests to catch missing mocks.

Flakiness usually comes from race conditions, missing async cleanup, or shared state between tests. Enable retries in CI, use waitFor for async assertions, capture traces on first retry, and reset database state between tests.

A common baseline is 80% for lines, functions, and statements, and 70% for branches, configured in Vitest's coverage thresholds so CI fails below them. Exclude config files, test helpers, barrel files, and entry points from measurement.