testing-tdd-london

vamseeachanta/testing-tdd-london

Coding

About

SKILL.md

Testing Tdd London

Quick Start

// 1. Start with acceptance test (outside)
describe('User Registration', () => {
  it('should register new user successfully', async () => {
    const mockRepository = { save: jest.fn().mockResolvedValue({ id: '123' }) };
    const mockNotifier = { sendWelcome: jest.fn() };

    const service = new UserService(mockRepository, mockNotifier);
    await service.register({ email: 'test@example.com' });

    // 2. Verify behavior (interactions)
    expect(mockRepository.save).toHaveBeenCalledWith(
      expect.objectContaining({ email: 'test@example.com' })
    );
    expect(mockNotifier.sendWelcome).toHaveBeenCalledWith('123');
  });
});

When to Use

Testing object collaborations and message passing
Contract-driven development with clear interfaces
Outside-in development starting from user behavior
When isolation of units is critical
Service orchestration testing
Testing HOW objects work together (not WHAT they contain)

Prerequisites

Understanding of mock objects vs stubs
Jest, Vitest, or similar testing framework with mocking support
Clear separation of concerns in architecture
Dependency injection pattern in codebase

References

Version History

1.0.0 (2026-01-02): Initial release - converted from tdd-london-swarm agent

Sub-Skills

Testing Tdd London

Quick Start

// 1. Start with acceptance test (outside)
describe('User Registration', () => {
  it('should register new user successfully', async () => {
    const mockRepository = { save: jest.fn().mockResolvedValue({ id: '123' }) };
    const mockNotifier = { sendWelcome: jest.fn() };

    const service = new UserService(mockRepository, mockNotifier);
    await service.register({ email: 'test@example.com' });

    // 2. Verify behavior (interactions)
    expect(mockRepository.save).toHaveBeenCalledWith(
      expect.objectContaining({ email: 'test@example.com' })
    );
    expect(mockNotifier.sendWelcome).toHaveBeenCalledWith('123');
  });
});

When to Use

Testing object collaborations and message passing
Contract-driven development with clear interfaces
Outside-in development starting from user behavior
When isolation of units is critical
Service orchestration testing
Testing HOW objects work together (not WHAT they contain)