Tdd Workflow

TDD Workflow Skill — Test-First Development

This skill enforces a strict Test-Driven Development workflow ensuring every line of production code is justified by a failing test.

The TDD Cycle

Copy code
┌─────────────────────────────────────────────┐
│                                             │
│   ┌─────────┐    ┌─────────┐    ┌────────┐ │
│   │  RED    │───▶│  GREEN  │───▶│REFACTOR│ │
│   │Write    │    │Make it  │    │Clean it│ │
│   │Failing  │    │Pass     │    │Up      │ │
│   └─────────┘    └─────────┘    └────────┘ │
│        │                              │     │
│        └──────────────────────────────┘     │
│                  REPEAT                     │
└─────────────────────────────────────────────┘

Test Categories

Unit Tests (Foundation)

• Test a single function/method in isolation
• Mock all external dependencies
• Fast (< 10ms per test)
• No file system, network, or database access

typescriptCopy code
describe('calculateTotal', () => {
  it('should sum all item prices', () => {
    const items = [{ price: 10 }, { price: 20 }, { price: 30 }];
    expect(calculateTotal(items)).toBe(60);
  });

  it('should return 0 for empty array', () => {
    expect(calculateTotal([])).toBe(0);
  });

  it('should handle negative prices with absolute value', () => {
    const items = [{ price: -10 }];
    expect(calculateTotal(items)).toBe(10);
  });
});

Integration Tests (Service Boundaries)

• Test interaction between modules
• Use real implementations where possible
• Use test databases/containers for data layer
• Verify contracts between services

E2E Tests (User Journeys)

• Test complete user workflows
• Run against real environment
• Minimal mocking
• Focus on critical paths

What to Test

For Every Function

For Every API Endpoint

Coverage Strategy

Must Have (100% coverage target)

• Business logic and domain rules
• Data transformations and validations
• Error handling paths
• Authentication and authorization

Should Have (80% coverage target)

• Controller/route handlers
• Service orchestration
• Data access layer

Nice to Have (60% coverage target)

• Configuration loading
• Utility functions
• Logging and monitoring

Test Quality Rules

1. No Test Interdependence: Each test must run independently
2. Descriptive Names: it('should return 404 when user not found')
3. Arrange-Act-Assert: Clear three-phase structure
4. One Assertion Per Concept: Group related assertions, separate unrelated
5. Deterministic: Same test, same result, every time
6. Fast Feedback: Unit tests < 10ms, Integration < 1s, E2E < 30s

When NOT to Use

Do NOT use this skill when:

• Working on existing code without tests (use debugging skill to understand first)
• Designing database schemas (use database-design skill)
• Writing API endpoint implementations (use api-design skill)
• Reviewing code for quality issues (use code-review skill)
• Performing security audits (use security-auditor skill)
• Analyzing deployment configurations (use deployment skill)
• Designing multi-page website layouts (use design-system skill)
• Reviewing git workflows (use git-workflow skill)