testing-tdd-london-mock-management

name	testing-tdd-london-mock-management
description	Sub-skill of testing-tdd-london: Mock Management (+2).
version	1.0.0
category	development
type	reference
scripts_exempt	true

Mock Management (+2)

Mock Management

• Keep mocks simple and focused on single behavior
• Verify interactions, not implementation details
• Use jest.fn() for behavior verification
• Avoid over-mocking internal details
• Reset mocks between tests

Contract Design

• Define clear interfaces through mock expectations
• Focus on object responsibilities and collaborations
• Use mocks to DRIVE design decisions
• Keep contracts minimal and cohesive

Common Pitfalls

// BAD: Over-mocking internal details
const mock = {
  _internalState: {},
  _privateMethod: jest.fn()  // Don't mock private methods
};

// GOOD: Mock only public interface
const mock = {
  publicMethod: jest.fn().mockReturnValue(expectedResult)
};

// BAD: Verifying too many implementation details
expect(mock.method).toHaveBeenCalledTimes(3);  // Fragile

// GOOD: Verify essential behavior
expect(mock.method).toHaveBeenCalledWith(expectedArgs);