Testing & Debugging Interview Questions

Setup using @testing-library/react, MockedProvider. Configure test wrappers, mock responses. Features: mock Apollo Client, query mocking. Essential for unit and integration testing.

MockedProvider enables Apollo Client testing. Provides mock responses, error simulation. Features: request matching, response timing control. Essential for component testing.

Query testing through mock responses, assertion utilities. Test loading states, error handling. Features: response timing, cache behavior. Verify data fetching logic.

Mutation testing through mock functions, result verification. Test optimistic updates, error scenarios. Features: cache updates, response handling. Verify data modification logic.

Cache debugging through Apollo DevTools, cache inspection. Monitor cache updates, state changes. Features: cache explorer, query watcher. Essential for troubleshooting.

Error testing through mock errors, response simulation. Test error handling, recovery logic. Features: network errors, GraphQL errors. Verify error handling implementation.

Integration testing through test utilities, component rendering. Test component interactions, data flow. Features: full rendering, async testing. Verify component integration.

Debugging tools: Apollo DevTools, React DevTools, Network inspector. Monitor queries, cache state, performance. Features: request tracking, state inspection. Essential for development.

Cache policy testing through mock operations, state verification. Test cache behavior, updates. Features: field policies, type policies. Verify cache configuration.

Mocking practices: realistic data, proper typing. Implement consistent mocks, error cases. Features: type generation, schema validation. Ensure reliable test data.

Optimistic response testing through update verification, timing checks. Test UI updates, rollbacks. Features: cache inspection, state tracking. Verify optimistic behavior.

Snapshot testing captures component output. Compare rendered content, query results. Features: automated comparison, update mechanism. Verify rendering consistency.

Network debugging through request inspection, response analysis. Monitor headers, payload data. Features: request tracking, error detection. Verify API communication.

Subscription testing through mock WebSocket, event simulation. Test real-time updates, connection handling. Features: subscription mocking, event verification. Verify real-time behavior.

Performance testing through metrics collection, timing analysis. Test query execution, cache efficiency. Features: performance tracking, optimization verification. Verify system performance.

Cache debugging through state inspection, update tracking. Identify inconsistencies, normalization issues. Features: cache comparison, update verification. Resolve cache problems.

Local state testing through resolver verification, cache inspection. Test field policies, local mutations. Features: state management, update validation. Verify local operations.

Error boundary testing through error simulation, recovery verification. Test fallback UI, error handling. Features: error capture, component recovery. Verify error management.

Variable debugging through request inspection, value tracking. Monitor variable usage, type validation. Features: variable inspection, value verification. Resolve query issues.

Testing utilities include MockedProvider, test renderers. Provide mock data, assertion helpers. Features: component testing, query simulation. Essential for test implementation.

E2E testing through Cypress, TestCafe integration. Test full application flow, user scenarios. Features: full stack testing, integration verification. Verify system functionality.

Mutation debugging through update tracking, result verification. Monitor cache changes, optimistic updates. Features: mutation tracking, state verification. Resolve update issues.

Pagination testing through data loading verification, cache updates. Test fetch more functionality, cursor handling. Features: load testing, cache behavior. Verify pagination logic.

Common pitfalls: improper mocking, async handling issues. Address timing problems, cache management. Features: test isolation, proper setup. Avoid testing antipatterns.

Fragment debugging through composition analysis, reuse verification. Monitor fragment spreading, type conditions. Features: fragment inspection, usage tracking. Resolve fragment issues.

Error handling testing through scenario simulation, recovery verification. Test error states, user feedback. Features: error testing, handling validation. Verify error management.

Mock schema through type definitions, resolvers. Implement test data, response patterns. Features: schema simulation, type checking. Essential for isolated testing.

Cache policy debugging through policy inspection, behavior analysis. Monitor field policies, type policies. Features: policy tracking, update verification. Resolve policy issues.

Reactive variable testing through value tracking, update verification. Test reactivity, dependency updates. Features: state management, update validation. Verify reactive behavior.

Component testing practices: isolation, proper mocking. Implement realistic scenarios, error cases. Features: component rendering, interaction testing. Ensure reliable tests.