cf-tdd

The cf-tdd skill automatically activates when you're writing new code. It enforces the test-driven development (TDD) discipline: write a failing test first, implement minimal code to pass it, then refactor.

When It Activates

Automatically triggered when:

• Creating new functions or methods
• Adding new modules or classes
• Writing feature code from scratch
• Test file exists but implementation doesn't

The TDD Cycle

RED: Write Failing Test

Start by writing a test that describes desired behavior—it fails because the code doesn't exist yet.

// test/user.test.ts
test('should hash password with bcrypt', () => {
  const password = 'secret123';
  const hashed = hashPassword(password);
  expect(hashed).not.toBe(password);
  expect(hashed.length).toBeGreaterThan(10);
});

GREEN: Implement Minimal Code

Write the simplest code that makes the test pass. No over-engineering.

// src/user.ts
export function hashPassword(password: string): string {
  // Minimal implementation to pass test
  return 'hashed_' + password;
}

REFACTOR: Improve Code

Now improve the code while keeping tests green.

// src/user.ts
import bcrypt from 'bcrypt';

export function hashPassword(password: string): string {
  return bcrypt.hashSync(password, 10);
}

Benefits

• Confidence — Tests ensure code works before production
• Design — Writing tests first leads to better API design
• Coverage — Most code has tests automatically
• Refactoring — Safe to improve code with test safety net
• Documentation — Tests serve as usage examples

When It Helps Most

• Complex business logic
• Data transformations
• Critical paths (auth, payments)
• Edge case handling
• Error scenarios

Key Rules

1. Always test first — No code without failing test
2. Keep tests simple — Each test validates one behavior
3. One assert per test — Clear pass/fail indication
4. Test edge cases — Null, empty, invalid input
5. Refactor freely — Tests prevent regressions