Frontend unit and end-to-end testing strategy

Interview framing: Testing should protect important behavior without making refactors painful. The pyramid is useful, but product risk matters more than dogma.

Testing layers:

1. Unit tests:

• Pure functions, reducers, validators, formatters, permissions, and state transitions.
• Fast and stable.

2. Component tests:

• Render a component and interact with it like a user.
• Assert visible behavior, not implementation details.

3. Integration tests:

• Verify components, routing, API clients, and state management work together.
• Mock network at the boundary.

4. End-to-end tests:

• Cover critical user journeys: login, search, save, dashboard workflows.
• Fewer tests, high confidence, run in CI and before releases.

5. Accessibility:

• Add automated checks for labels, roles, contrast, keyboard flow where possible.
• Manually test important keyboard interactions.

Mocking strategy:

• Mock unstable external services.
• Prefer realistic fixtures and MSW-style request mocks over mocking every function.

What not to over-test:

• CSS implementation details.
• Framework internals.
• Snapshots that change often and catch little.

Good answer: "I want many cheap tests around logic, focused component tests around UI behavior, and a small number of E2E tests around business-critical flows."