mocking-network-and-time

Use page.route or context.route with a precise method-and-path matcher, then call route.fulfill with a realistic status, headers, and body. Register a catch-all route that throws on unmocked traffic so renamed endpoints fail loudly instead of passing through.

Use MSW for component and integration tests where handlers are shared across runners, and Playwright route for browser end-to-end tests since it sits below the application. Avoid running both on the same call; pick one interception layer per suite.

In Vitest call vi.useFakeTimers with vi.setSystemTime and restore with vi.useRealTimers in afterEach. In Playwright use page.clock.install with a fixed date, then fastForward or setFixedTime, and pin timezoneId and locale in the config.

No. End-to-end tests should keep your own stack real and mock only what you do not own, such as third-party APIs or payment providers. Mocking your own API in an E2E test turns it into an integration test and hides contract breaks.

The mock has drifted from the real dependency. Add a drift guard: a contract check against the real spec, a documented HAR refresh command, or a thin unmocked smoke test run on a schedule, and record when it was last verified.

Use HAR replay for end-to-end tests against a large read-only API surface you do not want to hand-write. Always set notFound to 'abort', strip secrets before committing, and treat a HAR older than the API's release cadence as expired.