Refactoring Safely

Safe refactoring strategies for Claude Code. Small steps, validated changes, easy rollback.

Quick Reference

The Safe Refactoring Loop

1. Verify tests pass (baseline)
2. Make ONE small change
3. Run tests
4. If tests pass: commit
5. If tests fail: revert and retry smaller
6. Repeat

Before Any Refactoring

Prerequisites Checklist

• All tests passing
• Working directory clean (git status)
• On feature branch (not main)
• Tests cover the code being refactored
• Understand what the code does

Create Baseline

# Ensure clean state
git status

# Run full test suite
bun test

# Create savepoint
git commit -m "chore: checkpoint before refactoring"

Common Refactoring Patterns

Extract Function/Method

When: Duplicate code, long functions, complex conditionals

// Before: Long function with embedded logic
function processOrder(order: Order) {
  // 20 lines of validation
  // 30 lines of processing
  // 10 lines of notification
}

// After: Extracted functions
function processOrder(order: Order) {
  validateOrder(order);
  executeOrder(order);
  notifyCustomer(order);
}

Safe Steps:

1. Identify code to extract
2. Create new function with parameters
3. Copy code to new function
4. Replace original with function call
5. Run tests
6. Commit

Rename Symbol

When: Name doesn't reflect purpose, inconsistent naming

// Before
const d = new Date();

// After
const createdAt = new Date();

Safe Steps:

1. Use IDE/editor rename refactoring if available
2. Or use search-and-replace with word boundaries
3. Check all references updated
4. Run tests
5. Commit

Move File/Module

When: Wrong directory, reorganizing structure

Safe Steps:

1. Update imports in the file being moved
2. Move file to new location
3. Update all import statements referencing the file
4. Run tests
5. Commit

Inline Function

When: Function does too little, unnecessary indirection

// Before
function isAdult(age: number) {
  return age >= 18;
}
const canVote = isAdult(user.age);

// After
const canVote = user.age >= 18;

Safe Steps:

1. Verify function has single call site (or few)
2. Copy function body to call site
3. Adjust variables as needed
4. Remove unused function
5. Run tests
6. Commit

Workflow: Basic Refactoring

Prerequisites

• Tests exist and pass
• Clean git state
• On feature branch

Steps

1. Establish Baseline

   • Run bun test - all pass
   • Create checkpoint commit

2. Plan Changes

   • Identify what to refactor
   • Choose ONE refactoring type
   • List affected files

3. Execute

   • Make the change
   • Run tests immediately
   • Fix any failures

4. Validate

   • All tests pass
   • Manual smoke test if needed
   • No behavior changes

5. Commit

   • Descriptive commit message
   • Reference issue if applicable

Validation

• Tests pass before and after
• Same functionality preserved
• Code is cleaner/clearer

Test Coverage Considerations

Before Refactoring

# Check coverage for files you'll touch
bun test --coverage

# Identify untested code
# Add tests for uncovered critical paths

Minimum Coverage for Safety

Adding Tests First

If coverage is low:

1. Write characterization tests (capture current behavior)
2. Don't fix bugs during refactoring
3. Document unexpected behavior for later

// Characterization test - captures current behavior
test('processOrder returns null for empty order', () => {
  // This might be a bug, but document it first
  expect(processOrder({})).toBeNull();
});

Rollback Strategies

Git-Based Rollback

# Undo last commit (keep changes staged)
git reset --soft HEAD~1

# Undo last commit (keep changes unstaged)
git reset HEAD~1

# Undo last commit (discard changes)
git reset --hard HEAD~1

# Revert specific commit (creates new commit)
git revert <commit-hash>

Stash-Based Recovery

# Save current work
git stash push -m "refactoring attempt 1"

# Try different approach
# ...

# If new approach fails, restore stash
git stash pop

Branch-Based Safety

# Create experimental branch
git checkout -b refactor/extract-auth-module

# Do refactoring work
# ...

# If successful, merge to feature branch
git checkout feature/my-feature
git merge refactor/extract-auth-module

# If failed, just delete the branch
git branch -D refactor/extract-auth-module

Common Mistakes

When to Stop Refactoring

• Tests are failing and you can't fix them quickly
• You're changing behavior, not just structure
• The refactoring scope is growing uncontrollably
• You're unsure what the code should do
• You've been refactoring the same area for hours

Stop, commit what works, and reassess.

Decision Guide: Which Refactoring?

Reference Files