What testing tools do you use?

The short answer

A typical modern testing setup includes: a test runner (Jest or Vitest), a component testing library (React Testing Library), a mocking library (built into Jest/Vitest), a code coverage tool (built into Jest/Vitest), and optionally an E2E framework (Playwright or Cypress). CI/CD integrates them all to run on every pull request.

A typical React testing stack

• Vitest or Jest — runs tests, provides assertions (expect), mocking (jest.fn), and coverage
• React Testing Library — renders components and queries the DOM like a user would
• user-event — simulates realistic user interactions (typing, clicking)
• MSW (Mock Service Worker) — intercepts network requests in tests without mocking fetch directly
• Playwright — end-to-end tests in real browsers

How they work together

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// Vitest + React Testing Library + user-event
import { render, screen } from '@testing-library/react';
import userEvent from '@testing-library/user-event';
test('submitting the form calls onSubmit', async () => {
  const handleSubmit = vi.fn();
  render(<ContactForm onSubmit={handleSubmit} />);
  await userEvent.type(
    screen.getByLabelText('Name'),
    'John'
  );
  await userEvent.click(screen.getByText('Submit'));
  expect(handleSubmit).toHaveBeenCalledWith({
    name: 'John',
  });
});

MSW for API mocking

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import { http, HttpResponse } from 'msw';
import { setupServer } from 'msw/node';
const server = setupServer(
  http.get('/api/users', () => {
    return HttpResponse.json([{ id: 1, name: 'John' }]);
  })
);
beforeAll(() => server.listen());
afterEach(() => server.resetHandlers());
afterAll(() => server.close());

MSW intercepts actual network requests, making your tests more realistic than mocking fetch directly.

CI/CD integration

Tests run automatically on every pull request:

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# GitHub Actions example
- run: npm test -- --coverage
- run: npx playwright test

Why interviewers ask this

This is a practical experience question. Interviewers want to see if you have a real testing workflow and know how different tools complement each other.