Testing & Debugging Interview Questions

Vitest is the recommended testing framework for Svelte applications. It's fast, provides good integration with SvelteKit, and supports component testing. Jest can also be used but requires additional configuration.

Component tests use @testing-library/svelte. Mount components using render method. Test component behavior and DOM updates. Example: import { render } from '@testing-library/svelte'; const { getByText } = render(Component);

Svelte Inspector is a development tool enabled with 'ctrl + shift + i'. Shows component hierarchy, props, state. Helps debug component structure and data flow. Available in development mode.

Async tests use async/await syntax. Test async operations using act function. Handle promises and timeouts. Example: await fireEvent.click(button); await findByText('result');

Testing matchers verify component state/behavior. Include toBeInTheDocument, toHaveTextContent, toBeVisible. Provided by @testing-library/jest-dom. Support custom matchers.

Store state can be debugged using $store syntax. Subscribe to store changes. Log state updates. Use Svelte devtools. Monitor store mutations.

Testing hierarchy includes unit tests, integration tests, end-to-end tests. Focus on component isolation. Test component interaction. Verify application flow.

Event handlers tested using fireEvent. Simulate user interactions. Verify event outcomes. Example: fireEvent.click(button); expect(result).toBe(expected);

Snapshot testing captures component output. Compares against stored snapshots. Detects UI changes. Example: expect(container).toMatchSnapshot();

Props testing verifies component behavior with different props. Test prop types and values. Handle prop updates. Verify component rendering.

Integration testing verifies component interaction. Test multiple components. Handle data flow. Implement test scenarios. Manage test environment.

Store testing verifies store behavior. Test store updates. Handle subscriptions. Implement store mock. Manage store state.

Test mocks simulate dependencies. Handle external services. Support mock responses. Implement mock behavior. Manage mock state.

Route testing verifies navigation behavior. Test route parameters. Handle route changes. Implement navigation tests. Manage route state.

Test fixtures provide test data. Handle data setup. Support test isolation. Implement fixture management. Manage fixture cleanup.

Animation testing verifies transition behavior. Test animation states. Handle animation timing. Implement animation checks. Manage animation events.

Test hooks handle test lifecycle. Support setup/teardown. Implement test utilities. Manage test state. Handle test dependencies.

Error handling testing verifies error states. Test error boundaries. Handle error recovery. Implement error scenarios. Manage error logging.

Test coverage tracks code coverage. Generate coverage reports. Set coverage targets. Implement coverage checks. Manage coverage gaps.

Test organization structures test files. Group related tests. Support test discovery. Implement naming conventions. Manage test hierarchy.

Advanced patterns include test factories, test builders. Handle complex scenarios. Support pattern composition. Implement testing strategies.

Test automation handles continuous testing. Set up CI/CD pipelines. Support automated runs. Implement test reporting. Manage test environments.

Performance testing measures component efficiency. Test rendering speed. Handle resource usage. Implement benchmarks. Manage performance metrics.

Accessibility testing verifies a11y compliance. Test screen readers. Handle keyboard navigation. Implement ARIA testing. Manage compliance reports.

Visual regression detects UI changes. Compare screenshots. Handle visual diffs. Implement image comparison. Manage baseline images.

Test monitoring tracks test execution. Handle test metrics. Support test analytics. Implement monitoring tools. Manage monitoring data.

Test documentation describes test cases. Generate documentation automatically. Support example tests. Manage documentation updates. Handle versioning.

Security testing verifies application security. Test vulnerability prevention. Handle security scenarios. Implement security checks. Manage security reports.

Load testing verifies application performance. Test under heavy load. Handle stress scenarios. Implement load simulation. Manage performance data.

Environment management handles test environments. Set up configurations. Support multiple environments. Implement environment isolation. Manage dependencies.