TDD Workflow Skill

This skill implements the Test-Driven Development (TDD) cycle: RED → GREEN → REFACTOR.

Purpose

Ensure all fixes are implemented following TDD principles, resulting in well-tested, high-quality code.

When to Use

• Implementing any bug fix
• Adding new functionality
• Modifying existing behavior

The TDD Cycle

    ┌─────────┐
    │   RED   │ Write a failing test
    └────┬────┘
         │
    ┌────▼────┐
    │  GREEN  │ Write minimal code to pass
    └────┬────┘
         │
    ┌────▼────┐
    │REFACTOR │ Clean up (optional)
    └────┬────┘
         │
         └────► Repeat if needed

Process

Phase 1: RED (Write Failing Test)

Objective: Create a test that reproduces the bug and fails.

1. Identify Test Location

   • Find existing test file OR
   • Create new test file following project conventions
   • Examples: *.test.ts, *.spec.js, test_*.py

2. Write Test Case

   // Example: Testing null check for user session
   describe('AuthService', () => {
     it('should handle expired session gracefully', () => {
       const auth = new AuthService();
       const expiredSession = { user: undefined };
       
       // This should NOT throw an error
       expect(() => auth.getCurrentUser(expiredSession)).not.toThrow();
       expect(auth.getCurrentUser(expiredSession)).toBeNull();
     });
   });
   

3. Run Tests - Verify Failure

   npm test  # or pytest, jest, etc.
   

   ⚠️ The test MUST fail - if it passes, the bug isn't reproduced correctly

4. Commit Test

   git add <test-files>
   git commit -m "test: add test for [bug description]"
   

Phase 2: GREEN (Implement Fix)

Objective: Write the minimum code to make the test pass.

1. Implement Minimal Fix

   // Before
   getCurrentUser(session: Session): User {
     return session.user.id;  // Crashes on undefined
   }
   
   // After (minimal fix)
   getCurrentUser(session: Session): User | null {
     if (!session.user) {
       return null;
     }
     return session.user.id;
   }
   

2. Run Tests - Verify Passing

   npm test
   

   ✅ All tests MUST pass - new test and existing tests

3. Commit Fix

   git add <source-files>
   git commit -m "fix: [description] ([issue-key])"
   

Phase 3: REFACTOR (Optional)

Objective: Clean up code while keeping tests green.

1. Identify Improvements

   • Remove duplication
   • Improve naming
   • Extract methods/functions
   • Simplify logic

2. Refactor in Small Steps

   • Make one change at a time
   • Run tests after each change
   • Ensure all tests still pass

3. Commit Refactoring (if significant)

   git add <files>
   git commit -m "refactor: [description]"
   

Verification Checklist

Before completing the TDD cycle:

• New test(s) written and passing
• All existing tests still pass
• Code follows project patterns
• No linting errors
• Commits use conventional format

Output Format

{
  "phase": "red|green|refactor|complete",
  "test_results": {
    "new_tests": 2,
    "total_tests": 150,
    "passed": 150,
    "failed": 0
  },
  "commits": [
    {
      "phase": "red",
      "sha": "abc123",
      "message": "test: add test for expired session handling"
    },
    {
      "phase": "green",
      "sha": "def456",
      "message": "fix: add null check for user session (PROJ-123)"
    }
  ],
  "status": "success|failed",
  "errors": []
}

Common Patterns

Testing for Exceptions

it('should throw on invalid input', () => {
  expect(() => validateEmail('')).toThrow('Email required');
});

Testing Async Code

it('should fetch user data', async () => {
  const user = await userService.fetch('123');
  expect(user.name).toBe('John');
});

Testing Edge Cases

it('should handle null input', () => { /* ... */ });
it('should handle empty array', () => { /* ... */ });
it('should handle max value', () => { /* ... */ });

Error Handling

Important

• NEVER skip the RED phase - always start with a failing test
• Keep changes minimal in GREEN phase
• Run tests frequently - after every change
• If stuck, ask for help - don't force incorrect code
• Tests are documentation - make them readable