testing-patterns

name	testing-patterns
description	Testing patterns including AAA, mocking, and test data management. Use when writing unit tests, integration tests, or test suites.
license	Apache 2.0

Testing Patterns

When to Use This Skill

• Writing unit tests
• Writing integration tests
• Setting up test infrastructure

Core Concepts

AAA Pattern (Arrange-Act-Assert)

describe('UserService', () => {
  describe('createUser', () => {
    it('should create user with valid data', async () => {
      // Arrange
      const createDto = { email: '[e-mail]', name: 'Test' };
      
      // Act
      const result = await service.createUser(createDto);
      
      // Assert
      expect(result).toBeDefined();
      expect(result.email).toBe(createDto.email);
    });
  });
});

Mocking

const mockRepository = {
  findById: jest.fn(),
  create: jest.fn(),
} as jest.Mocked<UserRepository>;

mockRepository.findById.mockResolvedValue({ id: '123' });

Test Data Factory

const userFactory = {
  valid: () => ({ email: '[e-mail]', name: 'Test' }),
  withEmail: (email: string) => ({ ...userFactory.valid(), email }),
  invalid: () => ({ email: 'invalid', name: '' }),
};

Test Naming

// Good: Describes scenario and expectation
it('should return 404 when user not found', async () => { ... });
it('should reject invalid email format', () => { ... });

// Bad
it('should work', () => { ... });

References

• Jest Documentation
• Playwright Documentation