TDD Refactor Phase

Refactor code with confidence using comprehensive test safety net:

[Extended thinking: This tool uses the tdd-orchestrator agent (opus model) for sophisticated refactoring while maintaining all tests green. It applies design patterns, improves code quality, and optimizes performance with the safety of comprehensive test coverage.]

Usage

Use Task tool with subagent_type="tdd-orchestrator" to perform safe refactoring.

Prompt: "Refactor this code while keeping all tests green: $ARGUMENTS. Apply TDD refactor phase:

Core Process

1. Pre-Assessment

• -Run tests to establish green baseline
• -Analyze code smells and test coverage
• -Document current performance metrics
• -Create incremental refactoring plan

2. Code Smell Detection

• -Duplicated code → Extract methods/classes
• -Long methods → Decompose into focused functions
• -Large classes → Split responsibilities
• -Long parameter lists → Parameter objects
• -Feature Envy → Move methods to appropriate classes
• -Primitive Obsession → Value objects
• -Switch statements → Polymorphism
• -Dead code → Remove

3. Design Patterns

• -Apply Creational (Factory, Builder, Singleton)
• -Apply Structural (Adapter, Facade, Decorator)
• -Apply Behavioral (Strategy, Observer, Command)
• -Apply Domain (Repository, Service, Value Objects)
• -Use patterns only where they add clear value

4. SOLID Principles

• -Single Responsibility: One reason to change
• -Open/Closed: Open for extension, closed for modification
• -Liskov Substitution: Subtypes substitutable
• -Interface Segregation: Small, focused interfaces
• -Dependency Inversion: Depend on abstractions

5. Refactoring Techniques

• -Extract Method/Variable/Interface
• -Inline unnecessary indirection
• -Rename for clarity
• -Move Method/Field to appropriate classes
• -Replace Magic Numbers with constants
• -Encapsulate fields
• -Replace Conditional with Polymorphism
• -Introduce Null Object

6. Performance Optimization

• -Profile to identify bottlenecks
• -Optimize algorithms and data structures
• -Implement caching where beneficial
• -Reduce database queries (N+1 elimination)
• -Lazy loading and pagination
• -Always measure before and after

7. Incremental Steps

• -Make small, atomic changes
• -Run tests after each modification
• -Commit after each successful refactoring
• -Keep refactoring separate from behavior changes
• -Use scaffolding when needed

8. Architecture Evolution

• -Layer separation and dependency management
• -Module boundaries and interface definition
• -Event-driven patterns for decoupling
• -Database access pattern optimization

9. Safety Verification

• -Run full test suite after each change
• -Performance regression testing
• -Mutation testing for test effectiveness
• -Rollback plan for major changes

10. Advanced Patterns

• -Strangler Fig: Gradual legacy replacement
• -Branch by Abstraction: Large-scale changes
• -Parallel Change: Expand-contract pattern
• -Mikado Method: Dependency graph navigation

Output Requirements

• -Refactored code with improvements applied
• -Test results (all green)
• -Before/after metrics comparison
• -Applied refactoring techniques list
• -Performance improvement measurements
• -Remaining technical debt assessment

Safety Checklist

Before committing:

• -✓ All tests pass (100% green)
• -✓ No functionality regression
• -✓ Performance metrics acceptable
• -✓ Code coverage maintained/improved
• -✓ Documentation updated

Recovery Protocol

If tests fail:

• -Immediately revert last change
• -Identify breaking refactoring
• -Apply smaller incremental changes
• -Use version control for safe experimentation

Example: Extract Method Pattern

Before:

class OrderProcessor {
  processOrder(order: Order): ProcessResult {
    // Validation
    if (!order.customerId || order.items.length === 0) {
      return { success: false, error: "Invalid order" };
    }

    // Calculate totals
    let subtotal = 0;
    for (const item of order.items) {
      subtotal += item.price * item.quantity;
    }
    let total = subtotal + (subtotal * 0.08) + (subtotal > 100 ? 0 : 15);

    // Process payment...
    // Update inventory...
    // Send confirmation...
  }
}

After:

class OrderProcessor {
  async processOrder(order: Order): Promise<ProcessResult> {
    const validation = this.validateOrder(order);
    if (!validation.isValid) return ProcessResult.failure(validation.error);

    const orderTotal = OrderTotal.calculate(order);
    const inventoryCheck = await this.inventoryService.checkAvailability(order.items);
    if (!inventoryCheck.available) return ProcessResult.failure(inventoryCheck.reason);

    await this.paymentService.processPayment(order.paymentMethod, orderTotal.total);
    await this.inventoryService.reserveItems(order.items);
    await this.notificationService.sendOrderConfirmation(order, orderTotal);

    return ProcessResult.success(order.id, orderTotal.total);
  }

  private validateOrder(order: Order): ValidationResult {
    if (!order.customerId) return ValidationResult.invalid("Customer ID required");
    if (order.items.length === 0) return ValidationResult.invalid("Order must contain items");
    return ValidationResult.valid();
  }
}

Applied: Extract Method, Value Objects, Dependency Injection, Async patterns

Code to refactor: $ARGUMENTS"