testing

Configure vitest.config.ts with globals enabled, jsdom or node environment, a setup file, and v8 coverage provider. Add path aliases via the resolve option, then write tests using describe/it/expect with descriptive names for each behavior.

Playwright is recommended for multi-browser support, faster execution, and better developer experience. It includes built-in screenshots, trace capture on retry, and parallel execution across Chromium, Firefox, and mobile device profiles.

Define default handlers with http.get and HttpResponse.json, then start a setupServer instance in beforeAll. Override handlers per-test with server.use() for error cases, and reset handlers in afterEach to isolate tests.

The testing trophy prioritizes integration tests over unit tests because they catch bugs that matter at module boundaries. E2E tests cover only critical paths like auth and checkout, while unit tests handle pure logic and static analysis runs free.

Flakiness usually comes from hard-coded timeouts and race conditions. Use expect-based waiting and accessible selectors like getByRole instead of fixed delays, enable retries only in CI, and capture traces on first retry for debugging.

Avoid testing third-party library internals, implementation details like state shape, CSS styling, and framework lifecycle methods. Focus tests on business logic, user interactions, error states, API contracts, and accessibility roles.