developing-test-driven

name: developing-test-driven description: AI agent practices test-first development with the Red-Green-Refactor cycle for confident, well-designed code. Use when implementing features, fixing bugs, or establishing testing practices. category: methodology related_skills: - methodology/test-enforcement - methodology/test-task-generation - testing/vitest - testing/pytest related_commands: - /dev:tdd - /dev:feature-tested - /dev:test-write - /quality:verify-done

Developing Test-Driven

Quick Start

1. Red - Write a failing test that defines desired behavior
2. Green - Write minimal code to make the test pass
3. Refactor - Improve code while keeping tests green
4. Repeat - Continue with next behavior (1-5 minute cycles)

Features

Common Patterns

// RED-GREEN-REFACTOR CYCLE

// RED: Write failing test
it('rejects passwords shorter than 8 characters', () => {
  const result = validatePassword('short');
  expect(result.valid).toBe(false);
  expect(result.errors).toContain('Password must be at least 8 characters');
});

// GREEN: Minimal implementation
function validatePassword(password: string) {
  const errors = [];
  if (password.length < 8) {
    errors.push('Password must be at least 8 characters');
  }
  return { valid: errors.length === 0, errors };
}

// REFACTOR: Extract rules (tests stay green)
const rules = [
  { test: (p) => p.length >= 8, message: 'Must be 8+ chars' },
  { test: (p) => /[A-Z]/.test(p), message: 'Must have uppercase' },
];
function validatePassword(password: string) {
  const errors = rules.filter(r => !r.test(password)).map(r => r.message);
  return { valid: errors.length === 0, errors };
}

// ARRANGE-ACT-ASSERT Pattern
it('increases total when item added', () => {
  // ARRANGE
  const cart = new ShoppingCart();
  const item = { id: '1', price: 10.00 };

  // ACT
  cart.addItem(item);

  // ASSERT
  expect(cart.total).toBe(10.00);
});

// PARAMETERIZED TESTS
it.each([
  ['simple@example.com', true],
  ['user.name@domain.org', true],
  ['invalid', false],
  ['@nodomain.com', false],
])('validates %s as %s', (email, expected) => {
  expect(isValidEmail(email)).toBe(expected);
});

// BUILDER PATTERN for test data
const user = new UserBuilder().admin().inactive().build();

# Mocking Guidelines
MOCK (external boundaries):
- External APIs (payment, email)
- Third-party services
- System clock, random
- Network requests

DON'T MOCK (your code):
- Pure functions
- Data transformations
- Business logic
- Internal services

# Coverage Analysis
| Type | Target | Notes |
|------|--------|-------|
| Statements | 80%+ | Code executed |
| Branches | 70%+ | If/else paths |
| Functions | 90%+ | All functions called |

REMEMBER: 100% coverage != well-tested
- Test edge cases
- Test error paths
- Test boundary conditions

Best Practices

Command Integration

Using TDD Command

# Start TDD workflow
/dev:tdd "user authentication"

# TDD with specific coverage
/dev:tdd "payment processing" --coverage 95

# TDD with specific test types
/dev:tdd "API endpoint" --test-types unit,integration,contract

Configuration

# .omgkit/workflow.yaml
testing:
  enabled: true
  enforcement:
    level: strict  # TDD recommends strict
  coverage_gates:
    unit:
      minimum: 90
      target: 95

Related Skills

• methodology/test-enforcement - Enforce test completion
• methodology/test-task-generation - Auto-generate test tasks
• methodology/testing-anti-patterns - Avoid common test mistakes
• testing/vitest - Vitest testing framework
• testing/playwright - E2E testing with Playwright