Green Phase: Simple function

def product_list(request): products = Product.objects.all() return JsonResponse({‘products’: list(products.values())})

Refactor: Class-based view

class ProductListView(View): def get(self, request): products = Product.objects.all() return JsonResponse({‘products’: list(products.values())})

Refactor: Generic view

class ProductListView(ListView): model = Product context_object_name = ‘products’

### Express Patterns

**Inline → Middleware → Service Layer:**
```javascript
// Green Phase: Inline logic
app.post('/api/users', (req, res) => {
  const user = { id: Date.now(), ...req.body };
  users.push(user);
  res.json(user);
});

// Refactor: Extract middleware
app.post('/api/users', validateUser, (req, res) => {
  const user = userService.create(req.body);
  res.json(user);
});

// Refactor: Full layering
app.post('/api/users',
  validateUser,
  asyncHandler(userController.create)
);

Use this skill when

• Moving from red to green in a TDD cycle
• Implementing minimal behavior to satisfy tests
• You want to keep implementation intentionally simple

Do not use this skill when

• You are refactoring for design or performance
• Tests are already passing and you need new requirements
• You need a full architectural redesign

Instructions

1. Review failing tests and identify the smallest fix.
2. Implement the minimal change to pass the next test.
3. Run tests after each change to confirm progress.
4. Record shortcuts or debt for the refactor phase.

Safety

• Avoid bypassing tests to make them pass.
• Keep changes scoped to the failing behavior only.

Resources

• resources/implementation-playbook.md for detailed patterns and examples.