Sometimes the backend isn’t ready or isn’t reliable. That’s when mocking helps. You replace real API responses with fake ones. This lets you test the UI in a controlled way.

Use tools like WireMock, MSW, or Playwright’s route mocking. Set up responses that match what the real API would return. Then run your UI tests against that.

Mocking also helps you test error states. What happens if the API fails? What if it returns no data? These cases are hard to create with real servers.

Keep your mocks realistic. Use data that looks like production. Match status codes and delays too, if needed.

Mocking isn’t just for early development—it’s useful even in mature projects. It makes UI tests faster and more reliable.