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name: refactoring description: Refactoring assessment and patterns. Use after tests pass (GREEN phase) to assess improvement opportunities.

Refactoring

Refactoring is the third step of TDD. After GREEN, assess if refactoring adds value.

When to Refactor

• Always assess after green
• Only refactor if it improves the code
• Commit working code BEFORE refactoring (critical safety net)

Commit Before Refactoring - WHY

Having a working baseline before refactoring:

• Allows reverting if refactoring breaks things
• Provides safety net for experimentation
• Makes refactoring less risky
• Shows clear separation in git history

Workflow:

1. GREEN: Tests pass
2. COMMIT: Save working code
3. REFACTOR: Improve structure
4. COMMIT: Save refactored code

Priority Classification

Priority	Action	Examples
Critical	Fix now	Mutations, knowledge duplication, >3 levels nesting
High	This session	Magic numbers, unclear names, >30 line functions
Nice	Later	Minor naming, single-use helpers
Skip	Don't change	Already clean code

DRY = Knowledge, Not Code

Abstract when:

• Same business concept (semantic meaning)
• Would change together if requirements change
• Obvious why grouped together

Keep separate when:

• Different concepts that look similar (structural)
• Would evolve independently
• Coupling would be confusing

Example Assessment

// After GREEN:
const processOrder = (order: Order): ProcessedOrder => {
  const itemsTotal = order.items.reduce((sum, item) => sum + item.price, 0);
  const shipping = itemsTotal > 50 ? 0 : 5.99;
  return { ...order, total: itemsTotal + shipping, shippingCost: shipping };
};

// ASSESSMENT:
// ⚠️ High: Magic numbers 50, 5.99 → extract constants
// ✅ Skip: Structure is clear enough
// DECISION: Extract constants only

Speculative Code is a TDD Violation

If code isn't driven by a failing test, don't write it.

Key lesson: Every line must have a test that demanded its existence.

❌ Speculative code examples:

• "Just in case" logic
• Features not yet needed
• Code written "for future flexibility"
• Untested error handling paths

What to do: Delete speculative code. Add behavior tests instead.

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When NOT to Refactor

Don't refactor when:

• ❌ Code works correctly (no bug to fix)
• ❌ No test demands the change (speculative refactoring)
• ❌ Would change behavior (that's a feature, not refactoring)
• ❌ Premature optimization
• ❌ Code is "good enough" for current phase

Remember: Refactoring should improve code structure without changing behavior.

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Commit Messages for Refactoring

refactor: extract scenario validation logic
refactor: simplify error handling flow
refactor: rename ambiguous parameter names

Format: refactor: <what was changed>

Note: Refactoring commits should NOT be mixed with feature commits.

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Refactoring Checklist

• All tests pass without modification
• No new public APIs added
• Code more readable than before
• Committed separately from features
• Committed BEFORE refactoring (safety net)
• No speculative code added
• Behavior unchanged (tests prove this)