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:
- GREEN: Tests pass
- COMMIT: Save working code
- REFACTOR: Improve structure
- 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 onlySpeculative 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.
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.
Commit Messages for Refactoring
refactor: extract scenario validation logic
refactor: simplify error handling flow
refactor: rename ambiguous parameter namesFormat: refactor: <what was changed>
Note: Refactoring commits should NOT be mixed with feature commits.
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)