testing-tdd-london

name	testing-tdd-london
description	TDD London School (mockist) specialist for mock-driven, outside-in development. Use for behavior verification testing, contract-driven development, testing object collaborations, or when focusing on HOW objects interact rather than WHAT they contain.
version	1.0.0
category	development
type	hybrid
capabilities	["mock_driven_development","outside_in_tdd","behavior_verification","contract_testing","interaction_testing","swarm_test_coordination"]
tools	["Read","Write","Bash","Task"]
related_skills	["testing-production","planning-code-goal","webapp-testing"]
hooks	{"pre":"echo \"TDD London School session starting...\"\nif command -v npx >/dev/null 2>&1; then\n echo \"Coordinating with swarm test agents...\"\nfi\n","post":"echo \"London School TDD complete - mocks verified\"\nif [ -f \"package.json\" ]; then\n npm test --if-present\nfi\n"}
requires	[]
tags	[]

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: '[e-mail]' });

    // 2. Verify behavior (interactions)
    expect(mockRepository.save).toHaveBeenCalledWith(
      expect.objectContaining({ email: '[e-mail]' })
    );
    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