tdd-workflow

# Test-Driven Development Workflow

TDD is the foundation of verification-driven development. Write tests first, then implement code to make them pass.

## The Red-Green-Refactor Cycle

```
┌─────────────────────────────────────────────────────┐
│                                                     │
│   RED: Write failing test                           │
│         ↓                                           │
│   GREEN: Write minimal code to pass                 │
│         ↓                                           │
│   REFACTOR: Improve code while keeping tests green  │
│         ↓                                           │
│   (repeat)                                          │
│                                                     │
└─────────────────────────────────────────────────────┘
```

## Step-by-Step Process

### 1. RED - Write a Failing Test

```python
# tests/test_user_service.py
def test_create_user_returns_user_with_id():
    """Test that creating a user returns a user with an assigned ID."""
    service = UserService()

    user = service.create_user(name="Alice", email="alice@example.com")

    assert user.id is not None
    assert user.name == "Alice"
    assert user.email == "alice@example.com"
```

Run test to confirm it fails:
```bash
uv run pytest tests/test_user_service.py::test_create_user_returns_user_with_id -x
# Expected: FAILED (UserService doesn't exist)
```

### 2. GREEN - Minimal Implementation

Write just enough code to make the test pass:

```python
# src/user_service.py
from dataclasses import dataclass
import uuid

@dataclass
class User:
    id: str
    name: str
    email: str

class UserService:
    def create_user(self, name: str, email: str) -> User:
        return User(id=str(uuid.uuid4()), name=name, email=email)
```

Run test to confirm it passes:
```bash
uv run pytest tests/test_user_service.py::test_create_user_returns_user_with_id -x
# Expected: PASSED
```

### 3. REFACTOR - Improve While Green

Now improve the code (