Testing

Why this stage matters

Tests let you change code without fear, and they are how teams review AI-generated changes safely. Companies expect at least component and E2E testing experience from mid-level developers.

What to learn

1. Must know

   Unit & Component Tests

   Mark as done

   Vitest (or Jest) for logic, Testing Library for components, testing behaviour the user sees instead of implementation details.

   You're done when

   • Your component tests query by role and label, not by class name.
   • You can mock an API with MSW.

   Resources

   • VitestDocs
   • Testing LibraryDocs
   • MSWDocs
2. Must know

   End-to-End Tests

   Mark as done

   Playwright for critical user journeys across real browsers, including accessibility checks.

   You're done when

   • Your app's critical flow (sign up, checkout) has an E2E test that runs in CI.

   Resources

   • PlaywrightDocs

Common mistakes

• Chasing 100% coverage instead of testing what matters.
• Testing implementation details that break on every refactor.