PrepIQ

Testing React Applications

Q: How do you test async operations?

test('fetches data', async () => { render(<DataComponent />); const element = await screen.findByText(/data/i); expect(element).toBeInTheDocument(); });

Write solid unit and integration tests using Jest and React Testing Library. Mock API calls and user interactions.

Category: React · Total Questions: 7

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Q1. What are testing libraries for React?

Answer

Jest, React Testing Library, Enzyme, Cypress, Playwright.

Q2. How do you write unit tests for React components?

Answer

import { render, screen } from '@testing-library/react';

test('renders welcome message', () => {
  render(<Welcome />);
  const element = screen.getByText(/welcome/i);
  expect(element).toBeInTheDocument();
});

Q3. How do you test async operations?

Answer

test('fetches data', async () => {
  render(<DataComponent />);
  const element = await screen.findByText(/data/i);
  expect(element).toBeInTheDocument();
});

Q4. How do you test Redux?

Answer

Test reducers, actions, selectors separately. Use mock store for integration tests.

Q5. What is mocking and stubbing?

Answer

Mocking - replace real functions with fake ones. Stubbing - provide fake implementations.

Q6. How do you test hooks?

Answer

import { renderHook, act } from '@testing-library/react';
import { useCounter } from './useCounter';

test('counter increments', () => {
  const { result } = renderHook(() => useCounter());
  act(() => { result.current.increment(); });
  expect(result.current.count).toBe(1);
});