ReddRadar
Agent skill
mobile-testing
Write and run tests for React Native apps using Jest and React Native Testing Library. Use when creating tests, debugging failures, or setting up test infrastructure.
Install this agent skill to your Project
npx add-skill https://github.com/aiskillstore/marketplace/tree/main/skills/babakbar/mobile-testing
SKILL.md
Mobile Testing
Testing guide for React Native applications.
When to Use
- Writing unit tests for components or utilities
- Creating integration tests for features
- Setting up test infrastructure
- Debugging test failures
- Improving test coverage
Test Setup
# Install testing dependencies
npm install --save-dev jest @testing-library/react-native
# Add to package.json
{
"scripts": {
"test": "jest",
"test:watch": "jest --watch",
"test:coverage": "jest --coverage"
}
}
Component Test Template
import { render, fireEvent } from '@testing-library/react-native';
import { MyButton } from './MyButton';
describe('MyButton', () => {
it('renders correctly', () => {
const { getByText } = render(<MyButton title="Click me" />);
expect(getByText('Click me')).toBeTruthy();
});
it('calls onPress when pressed', () => {
const onPress = jest.fn();
const { getByText } = render(
<MyButton title="Click me" onPress={onPress} />
);
fireEvent.press(getByText('Click me'));
expect(onPress).toHaveBeenCalledTimes(1);
});
});
Hook Test Template
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);
});
});
Utility Test Template
import { formatDate } from './formatDate';
describe('formatDate', () => {
it('formats date correctly', () => {
const date = new Date('2025-01-15');
expect(formatDate(date)).toBe('2025-01-15');
});
it('handles invalid input', () => {
expect(() => formatDate(null)).toThrow();
});
});
Mocking Patterns
Mock External Module
jest.mock('expo-notifications', () => ({
scheduleNotificationAsync: jest.fn(),
}));
Mock Database
jest.mock('@/db/client', () => ({
db: {
select: jest.fn(),
insert: jest.fn(),
},
}));
Mock Navigation
jest.mock('expo-router', () => ({
useRouter: () => ({
push: jest.fn(),
back: jest.fn(),
}),
}));
Running Tests
# Run all tests
npm test
# Watch mode (auto-rerun on changes)
npm run test:watch
# With coverage report
npm run test:coverage
# Run specific test file
npm test -- MyComponent.test.tsx
# Update snapshots
npm test -- -u
Best Practices
- Test Behavior, Not Implementation: Test what users see and do
- Use
testIDfor Selection: More reliable than text matching - Mock External Dependencies: Keep tests isolated and fast
- Test Edge Cases: Empty states, errors, loading states
- Keep Tests Simple: One assertion per test when possible
- Clean Up: Use
beforeEach/afterEachfor setup/teardown
Common Patterns
Async Testing
it('loads data', async () => {
const { findByText } = render(<DataComponent />);
expect(await findByText('Loaded')).toBeTruthy();
});
Testing Forms
it('validates input', () => {
const { getByTestId, getByText } = render(<LoginForm />);
fireEvent.changeText(getByTestId('email-input'), 'invalid');
fireEvent.press(getByTestId('submit-button'));
expect(getByText('Invalid email')).toBeTruthy();
});
Testing Lists
it('renders list items', () => {
const items = [{ id: '1', name: 'Item 1' }];
const { getAllByTestId } = render(<ItemList items={items} />);
expect(getAllByTestId('list-item')).toHaveLength(1);
});
Troubleshooting
- Tests timing out: Increase timeout or check for unresolved promises
- Can't find element: Use
screen.debug()to see rendered output - Mock not working: Ensure mock is before import
- Async issues: Use
waitFororfindByqueries
Resources
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