Testing React Components Interview Questions

React Testing Library: 1) Works with Jest as test runner, 2) Provides utilities for testing React components, 3) Focuses on testing behavior over implementation, 4) Encourages accessibility-first testing, 5) Uses queries to find elements. Example: render(<Component />); expect(screen.getByText('text')).toBeInTheDocument();

Component rendering tests: 1) Use render function from Testing Library, 2) Query rendered elements, 3) Assert on element presence, 4) Check component content, 5) Verify proper props rendering. Example: const { getByText } = render(<Component prop={value} />);

Query types include: 1) getBy* for elements that should be present, 2) queryBy* for elements that might not exist, 3) findBy* for async elements, 4) getAllBy*, queryAllBy*, findAllBy* for multiple elements, 5) Role-based, text-based, and label-based queries.

User event testing: 1) Import userEvent from @testing-library/user-event, 2) Simulate user interactions, 3) Assert on resulting changes, 4) Handle async events, 5) Test form interactions. Example: await userEvent.click(button); expect(result).toBeVisible();

jest-dom provides: 1) DOM-specific matchers, 2) toBeInTheDocument(), 3) toHaveClass(), 4) toBeVisible(), 5) toHaveValue() and other UI-specific assertions. Enhances Jest for DOM testing.

Props testing includes: 1) Rendering with different prop values, 2) Testing prop type validation, 3) Verifying prop updates, 4) Testing default props, 5) Testing required props. Example: render(<Component testProp='value' />);

Form testing involves: 1) Input change simulation, 2) Form submission testing, 3) Validation testing, 4) Error message verification, 5) Form state testing. Use userEvent for input interactions.

Hook testing requires: 1) @testing-library/react-hooks, 2) renderHook utility, 3) Testing state updates, 4) Testing hook effects, 5) Testing custom hook logic. Example: const { result } = renderHook(() => useCustomHook());

Accessibility testing includes: 1) Role-based queries, 2) ARIA attribute testing, 3) Keyboard navigation testing, 4) Screen reader compatibility, 5) Color contrast verification. Ensures inclusive user experience.

State testing involves: 1) Triggering state updates, 2) Verifying state changes, 3) Testing state-dependent rendering, 4) Testing state transitions, 5) Async state updates. Focus on behavior over implementation.

Async testing includes: 1) Using findBy* queries, 2) Waiting for element changes, 3) Testing loading states, 4) Error state testing, 5) Data fetching verification. Example: await findByText('loaded content');

Context testing involves: 1) Wrapping components in providers, 2) Testing context updates, 3) Testing consumer behavior, 4) Multiple context interaction, 5) Context state changes.

Redux integration testing: 1) Providing store wrapper, 2) Testing connected components, 3) Dispatching actions, 4) Testing state updates, 5) Testing selectors. Use proper store setup.

Router testing includes: 1) MemoryRouter setup, 2) Route rendering verification, 3) Navigation testing, 4) Route parameter testing, 5) Route protection testing. Consider router context.

Dependencies testing: 1) Mocking external hooks, 2) Testing dependency interactions, 3) Testing error cases, 4) Testing cleanup, 5) Testing hook composition. Use proper isolation.

Error boundary testing: 1) Error simulation, 2) Fallback rendering, 3) Error recovery, 4) Props passing through boundaries, 5) Nested error boundaries. Test error handling.

Performance testing: 1) Render timing measurement, 2) Re-render optimization verification, 3) Memory leak detection, 4) React profiler integration, 5) Performance regression testing.

Composition testing: 1) Testing component hierarchies, 2) Props drilling verification, 3) Component interaction testing, 4) Render prop testing, 5) HOC testing. Test component relationships.

Side effect testing: 1) useEffect testing, 2) Cleanup verification, 3) External interaction testing, 4) Timing dependencies, 5) Side effect ordering. Consider effect dependencies.

Lifecycle testing: 1) Mount behavior testing, 2) Update verification, 3) Unmount cleanup testing, 4) State persistence, 5) Effect timing. Test component phases.

Advanced patterns: 1) Component test factories, 2) Reusable test utilities, 3) Custom render methods, 4) Test composition, 5) Shared test behaviors. Improve test maintainability.

Complex UI testing: 1) Multi-step interaction flows, 2) Conditional rendering paths, 3) State machine testing, 4) Animation testing, 5) Gesture handling. Test user scenarios.

Microservice integration: 1) Service communication testing, 2) API interaction verification, 3) Error handling, 4) State synchronization, 5) Service dependency management.

Scaling testing: 1) Large data set handling, 2) Performance with many components, 3) Memory optimization, 4) Render optimization, 5) Resource management. Test scalability limits.

Visual testing: 1) Screenshot comparison, 2) Layout verification, 3) Style regression testing, 4) Component visual states, 5) Responsive design testing. Use visual testing tools.

Security testing: 1) XSS prevention, 2) Data sanitization, 3) Authentication flows, 4) Authorization checks, 5) Secure props handling. Test security measures.

Advanced state testing: 1) Complex state machines, 2) State orchestration, 3) State synchronization, 4) Persistence testing, 5) State recovery scenarios. Test state complexity.

Monitoring testing: 1) Performance metrics, 2) Error tracking, 3) Usage analytics, 4) Resource monitoring, 5) Health checks. Test monitoring integration.

Stress testing: 1) Load testing components, 2) Resource limits testing, 3) Concurrent operation handling, 4) Error recovery under stress, 5) Performance degradation testing.