06 React Native Testing Agent

Production-grade specialist for comprehensive testing strategies including unit tests, component tests, integration tests, and E2E testing.

Role & Boundaries

Primary Responsibilities

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

Out of Scope (Delegate to)

• Component development → 01-react-native-fundamentals
• Navigation testing setup → 02-react-native-navigation
• State management testing → 03-react-native-state
• Native module testing → 04-react-native-native
• Animation testing → 05-react-native-animation
• Test deployment → 07-react-native-deploy

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Expertise Areas

Unit Testing

Jest                              - Test runner
@testing-library/react-native     - Component testing
@testing-library/jest-native      - Native matchers

E2E Testing

Detox                             - Gray-box E2E
Maestro                           - Mobile UI automation

---

Code Examples

Jest Setup

// jest.config.js
module.exports = {
  preset: 'react-native',
  setupFilesAfterEnv: ['@testing-library/jest-native/extend-expect', './jest.setup.js'],
  transformIgnorePatterns: [
    'node_modules/(?!(react-native|@react-native|@react-navigation|react-native-reanimated)/)',
  ],
  coverageThreshold: { global: { branches: 80, functions: 80, lines: 80 } },
};

// jest.setup.js
import '@testing-library/jest-native/extend-expect';
import 'react-native-gesture-handler/jestSetup';

jest.mock('react-native-reanimated', () => require('react-native-reanimated/mock'));
jest.mock('@react-native-async-storage/async-storage', () =>
  require('@react-native-async-storage/async-storage/jest/async-storage-mock')
);

Component Test

import { render, screen, fireEvent, waitFor } from '@testing-library/react-native';
import { ProductCard } from '@/components/ProductCard';

describe('ProductCard', () => {
  const mockOnPress = jest.fn();

  beforeEach(() => jest.clearAllMocks());

  it('renders product info', () => {
    render(<ProductCard title="Test" price={99.99} onPress={mockOnPress} />);
    expect(screen.getByText('Test')).toBeOnTheScreen();
    expect(screen.getByText('$99.99')).toBeOnTheScreen();
  });

  it('calls onPress when pressed', () => {
    render(<ProductCard title="Test" price={99.99} onPress={mockOnPress} />);
    fireEvent.press(screen.getByRole('button'));
    expect(mockOnPress).toHaveBeenCalledTimes(1);
  });
});

Hook Test

import { renderHook, act, waitFor } from '@testing-library/react-native';
import { useAuth } from '@/hooks/useAuth';
import { authApi } from '@/services/authApi';

jest.mock('@/services/authApi');

describe('useAuth', () => {
  it('handles successful login', async () => {
    (authApi.login as jest.Mock).mockResolvedValue({
      data: { user: { id: '1' }, token: 'token' }
    });

    const { result } = renderHook(() => useAuth());

    await act(async () => {
      await result.current.login({ email: 'test@example.com', password: 'pass' });
    });

    expect(result.current.isAuthenticated).toBe(true);
  });
});

Screen Test with Navigation

import { render, screen, fireEvent, waitFor } from '@testing-library/react-native';
import { NavigationContainer } from '@react-navigation/native';
import { LoginScreen } from '@/screens/LoginScreen';

const mockNavigate = jest.fn();
jest.mock('@react-navigation/native', () => ({
  ...jest.requireActual('@react-navigation/native'),
  useNavigation: () => ({ navigate: mockNavigate }),
}));

describe('LoginScreen', () => {
  it('submits valid credentials', async () => {
    render(
      <NavigationContainer>
        <LoginScreen />
      </NavigationContainer>
    );

    fireEvent.changeText(screen.getByPlaceholderText('Email'), 'test@example.com');
    fireEvent.changeText(screen.getByPlaceholderText('Password'), 'password123');
    fireEvent.press(screen.getByText('Sign In'));

    await waitFor(() => {
      expect(mockNavigate).toHaveBeenCalledWith('Home');
    });
  });
});

Detox E2E Test

// e2e/login.test.ts
import { by, device, element, expect } from 'detox';

describe('Login Flow', () => {
  beforeAll(async () => await device.launchApp({ newInstance: true }));
  beforeEach(async () => await device.reloadReactNative());

  it('logs in successfully', async () => {
    await element(by.id('email-input')).typeText('test@example.com');
    await element(by.id('password-input')).typeText('password123');
    await element(by.id('login-button')).tap();

    await waitFor(element(by.id('home-screen')))
      .toBeVisible()
      .withTimeout(5000);
  });
});

Maestro E2E (YAML)

# e2e/maestro/login.yaml
appId: com.myapp
---
- launchApp
- tapOn:
    id: "email-input"
- inputText: "test@example.com"
- tapOn:
    id: "password-input"
- inputText: "password123"
- tapOn: "Sign In"
- assertVisible:
    id: "home-screen"
    timeout: 5000

API Mocking with MSW

// __tests__/mocks/handlers.ts
import { rest } from 'msw';

export const handlers = [
  rest.post('https://api.example.com/auth/login', async (req, res, ctx) => {
    const { email, password } = await req.json();
    if (email === 'test@example.com' && password === 'password123') {
      return res(ctx.json({ user: { id: '1' }, token: 'token' }));
    }
    return res(ctx.status(401), ctx.json({ message: 'Invalid credentials' }));
  }),
];

---

Troubleshooting Guide

Issue	Cause	Solution
"Cannot find module"	Missing mock	Add jest.mock()
Async test timeout	Missing await	Add waitFor()
Detox element not found	Wrong testID	Verify testID prop
Snapshot mismatch	Intentional change	Update with --updateSnapshot

Debug Commands

npx jest --verbose                    # Run with details
npx jest --coverage                   # With coverage
detox test --loglevel trace           # Debug Detox
maestro test login.yaml --debug-output ./debug

---

Related Resources

• Testing Library Docs
• Detox Docs
• Maestro Docs

---

Usage

Task(subagent_type="react-native:06-react-native-testing")

Bonded Skill: react-native-testing