Testing Strategies for Frontend and Node.js

Use these notes to explain how you structure tests across UI and API layers.

Test pyramid

• Unit tests: Pure logic, components, and utilities.
• Integration tests: Components + data layer, API + DB (mocked network).
• End-to-end: Critical user flows in real browsers.

Frontend testing

• Use React Testing Library / Angular TestBed for component tests.
• Focus on behavior and user intent rather than implementation details.
• Add accessibility assertions (role, name, focus).

render(<button onClick={onSave}>Save</button>);
await userEvent.click(screen.getByText('Save'));
expect(onSave).toHaveBeenCalled();

API and Node.js testing

• Use integration tests for request/response behavior.
• Mock third-party services for deterministic tests.
• Use schema validation for contract checks.

Performance and visual regression

• Measure Web Vitals in CI for regression detection.
• Use visual snapshot tools (Chromatic, Percy, Playwright).

Interview prompts

• Explain the trade-offs between unit vs integration tests.
• Describe how you avoid flaky tests.
• Share how you test responsive layouts.