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PublishedOctober 26, 2026 at 02:08 PM

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version: "1.0.1" name: code-showcase-testing-patterns description: Jest testing patterns, factory functions, mocking strategies, and TDD workflow. Use when writing unit tests, creating test factories, or following TDD red-green-refactor cycle. risk: critical source: https://github.com/ChrisWiles/claude-code-showcase/tree/main/.claude/skills/testing-patterns source_repo: ChrisWiles/claude-code-showcase source_type: community date_added: 2026-07-01 license: MIT license_source: https://github.com/ChrisWiles/claude-code-showcase/blob/main/LICENSE

Testing Patterns and Utilities

When to Use

Use this skill when you need jest testing patterns, factory functions, mocking strategies, and TDD workflow. Use when writing unit tests, creating test factories, or following TDD red-green-refactor cycle.

Testing Philosophy

Test-Driven Development (TDD):

Write failing test FIRST
Implement minimal code to pass
Refactor after green
Never write production code without a failing test

Behavior-Driven Testing:

Test behavior, not implementation
Focus on public APIs and business requirements
Avoid testing implementation details
Use descriptive test names that describe behavior

Factory Pattern:

Create getMockX(overrides?: Partial<X>) functions
Provide sensible defaults
Allow overriding specific properties
Keep tests DRY and maintainable

Test Utilities

Custom Render Function

Create a custom render that wraps components with required providers:

typescript

// src/utils/testUtils.tsx
import { render } from '@testing-library/react-native';
import { ThemeProvider } from './theme';
export const renderWithTheme = (ui: React.ReactElement) => {
  return render(
    <ThemeProvider>{ui}</ThemeProvider>
  );
};

Usage:

typescript

import { renderWithTheme } from 'utils/testUtils';
import { screen } from '@testing-library/react-native';
it('should render component', () => {
  renderWithTheme(<MyComponent />);
  expect(screen.getByText('Hello')).toBeTruthy();
});

Factory Pattern

Component Props Factory

typescript

import { ComponentProps } from 'react';
const getMockMyComponentProps = (
  overrides?: Partial<ComponentProps<typeof MyComponent>>
) => {
  return {
    title: 'Default Title',
    count: 0,
    onPress: jest.fn(),
    isLoading: false,
    ...overrides,
  };
};
// Usage in tests
it('should render with custom title', () => {
  const props = getMockMyComponentProps({ title: 'Custom Title' });
  renderWithTheme(<MyComponent {...props} />);
  expect(screen.getByText('Custom Title')).toBeTruthy();
});

Data Factory

typescript

interface User {
  id: string;
  name: string;
  email: string;
  role: 'admin' | 'user';
}
const getMockUser = (overrides?: Partial<User>): User => {
  return {
    id: '123',
    name: 'John Doe',
    email: 'john@example.com',
    role: 'user',
    ...overrides,
  };
};
// Usage
it('should display admin badge for admin users', () => {
  const user = getMockUser({ role: 'admin' });
  renderWithTheme(<UserCard user={user} />);
  expect(screen.getByText('Admin')).toBeTruthy();
});

Mocking Patterns

Mocking Modules

typescript

// Mock entire module
jest.mock('utils/analytics');
// Mock with factory function
jest.mock('utils/analytics', () => ({
  Analytics: {
    logEvent: jest.fn(),
  },
}));
// Access mock in test
const mockLogEvent = jest.requireMock('utils/analytics').Analytics.logEvent;

Mocking GraphQL Hooks

typescript

jest.mock('./GetItems.generated', () => ({
  useGetItemsQuery: jest.fn(),
}));
const mockUseGetItemsQuery = jest.requireMock(
  './GetItems.generated'
).useGetItemsQuery as jest.Mock;
// In test
mockUseGetItemsQuery.mockReturnValue({
  data: { items: [] },
  loading: false,
  error: undefined,
});

Test Structure

typescript

describe('ComponentName', () => {
  beforeEach(() => {
    jest.clearAllMocks();
  });
  describe('Rendering', () => {
    it('should render component with default props', () => {});
    it('should render loading state when loading', () => {});
  });
  describe('User interactions', () => {
    it('should call onPress when button is clicked', async () => {});
  });
  describe('Edge cases', () => {
    it('should handle empty data gracefully', () => {});
  });
});

Query Patterns

typescript

// Element must exist
expect(screen.getByText('Hello')).toBeTruthy();
// Element should not exist
expect(screen.queryByText('Goodbye')).toBeNull();
// Element appears asynchronously
expect(await screen.findByText('Loaded')).toBeTruthy();

User Interaction Patterns

typescript

import { fireEvent, screen } from '@testing-library/react-native';
it('should submit form on button click', async () => {
  const onSubmit = jest.fn();
  renderWithTheme(<LoginForm onSubmit={onSubmit} />);
  fireEvent.changeText(screen.getByLabelText('Email'), 'user@example.com');
  fireEvent.changeText(screen.getByLabelText('Password'), 'password123');
  fireEvent.press(screen.getByTestId('login-button'));
  await waitFor(() => {
    expect(onSubmit).toHaveBeenCalled();
  });
});

Anti-Patterns to Avoid

Testing Mock Behavior Instead of Real Behavior

typescript

// Bad - testing the mock
expect(mockFetchData).toHaveBeenCalled();
// Good - testing actual behavior
expect(screen.getByText('John Doe')).toBeTruthy();

Not Using Factories

typescript

// Bad - duplicated, inconsistent test data
it('test 1', () => {
  const user = { id: '1', name: 'John', email: 'john@test.com', role: 'user' };
});
it('test 2', () => {
  const user = { id: '2', name: 'Jane', email: 'jane@test.com' }; // Missing role!
});
// Good - reusable factory
const user = getMockUser({ name: 'Custom Name' });

Best Practices

Always use factory functions for props and data
Test behavior, not implementation
Use descriptive test names
Organize with describe blocks
Clear mocks between tests
Keep tests focused - one behavior per test

Running Tests

bash

# Run all tests
npm test
 
# Run with coverage
npm run test:coverage
 
# Run specific file
npm test ComponentName.test.tsx

Integration with Other Skills

react-ui-patterns: Test all UI states (loading, error, empty, success)
systematic-debugging: Write test that reproduces bug before fixing

Limitations

Use this skill only when the task clearly matches its upstream source and local project context.
Verify commands, generated code, dependencies, credentials, and external service behavior before applying changes.
Do not treat examples as a substitute for environment-specific tests, security review, or user approval for destructive or costly actions.

← v1.0.0 All versions