React Native Testing Skill

Learn comprehensive testing strategies including unit tests, component tests, and E2E tests.

Prerequisites

• React Native basics
• Understanding of async/await
• Familiarity with testing concepts

Learning Objectives

After completing this skill, you will be able to:

• Configure Jest for React Native
• Write component tests with Testing Library
• Mock native modules and APIs
• Implement E2E tests with Detox/Maestro
• Set up CI/CD test pipelines

---

Topics Covered

1. Jest Setup

// jest.config.js
module.exports = {
  preset: 'react-native',
  setupFilesAfterEnv: ['@testing-library/jest-native/extend-expect'],
  transformIgnorePatterns: [
    'node_modules/(?!(react-native|@react-native)/)',
  ],
};

2. Component Testing

import { render, screen, fireEvent } from '@testing-library/react-native';
import { Button } from './Button';

describe('Button', () => {
  it('calls onPress when pressed', () => {
    const onPress = jest.fn();
    render(<Button title="Click" onPress={onPress} />);

    fireEvent.press(screen.getByText('Click'));

    expect(onPress).toHaveBeenCalled();
  });
});

3. Hook Testing

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

describe('useCounter', () => {
  it('increments count', () => {
    const { result } = renderHook(() => useCounter());

    act(() => result.current.increment());

    expect(result.current.count).toBe(1);
  });
});

4. Mocking

// Mock native module
jest.mock('@react-native-async-storage/async-storage', () => ({
  setItem: jest.fn(),
  getItem: jest.fn(),
}));

// Mock API
jest.mock('./api', () => ({
  fetchUser: jest.fn().mockResolvedValue({ id: '1', name: 'Test' }),
}));

5. E2E with Detox

describe('Login', () => {
  beforeAll(async () => {
    await device.launchApp();
  });

  it('should login successfully', async () => {
    await element(by.id('email')).typeText('test@example.com');
    await element(by.id('password')).typeText('password');
    await element(by.id('login-btn')).tap();

    await expect(element(by.id('home'))).toBeVisible();
  });
});

---

Quick Start Example

// ProductCard.test.tsx
import { render, screen, fireEvent } from '@testing-library/react-native';
import { ProductCard } from './ProductCard';

const mockProduct = {
  id: '1',
  title: 'Test Product',
  price: 99.99,
};

describe('ProductCard', () => {
  it('renders product info', () => {
    render(<ProductCard {...mockProduct} onPress={jest.fn()} />);

    expect(screen.getByText('Test Product')).toBeOnTheScreen();
    expect(screen.getByText('$99.99')).toBeOnTheScreen();
  });

  it('handles press', () => {
    const onPress = jest.fn();
    render(<ProductCard {...mockProduct} onPress={onPress} />);

    fireEvent.press(screen.getByRole('button'));

    expect(onPress).toHaveBeenCalledWith('1');
  });
});

---

Common Errors & Solutions

Error	Cause	Solution
"Cannot find module"	Missing mock	Add jest.mock()
Async timeout	Missing await	Use waitFor()
Element not found	Wrong query	Check testID/role

---

Validation Checklist

• Unit tests pass
• Component tests cover interactions
• E2E tests complete flows
• Coverage meets threshold (80%+)

---

Usage

Skill("react-native-testing")

Bonded Agent: 06-react-native-testing