Safe Refactor — Behavioral Specification for Secure Code Restructuring

┌─────────────────────────────────────────────────────┐
│                    SAFE REFACTOR                     │
│                                                     │
│    Existing Tests ─────┐                            │
│                        ├──► SAFE TO REFACTOR        │
│    Coverage Good? ─────┘                            │
│                                                     │
│    Existing Tests ─────┐                            │
│                        ├──► ADD TESTS FIRST         │
│    Coverage Poor? ─────┘                            │
└─────────────────────────────────────────────────────┘

Behavioral Specification

Phase 1: Refactor Readiness Assessment

Before touching any code, answer these questions:

1.1 Why Are You Refactoring?

1.2 What Will Change?

Map out the scope:

## Refactoring Scope

### High-Risk Changes (Require Extra Care)
- [ ] Changing function signatures
- [ ] Moving code between modules
- [ ] Changing data structures
- [ ] Modifying shared utilities

### Medium-Risk Changes
- [ ] Extracting functions
- [ ] Renaming variables
- [ ] Reordering code

### Low-Risk Changes
- [ ] Formatting
- [ ] Comment improvements
- [ ] Renaming (non-shared)

1.3 What's the Blast Radius?

# Find all usages
grep -r "functionName" --include="*.ts" src/

# Check if it's a shared utility
# Check how many files depend on it

Phase 2: Test Coverage Verification

2.1 Test Coverage Check

## Current Test Coverage Analysis

| Module | Coverage | Tests | Action |
|--------|----------|-------|--------|
| utils.ts | 45% | 2 | Add tests before refactor |
| auth.ts | 89% | 12 | Safe to refactor |
| payment.ts | 0% | 0 | MUST add tests first |

2.2 Critical Path Identification

Before refactoring, identify what's MOST important to keep working:

┌────────────────────────────────────────────────────────────┐
│                    CRITICAL PATH MAP                       │
│                                                             │
│    User ──► Login ──► Dashboard ──► Action ──► Result     │
│                    │              │                        │
│                    │              └──► Analytics           │
│                    │                                     │
│                    └──► Notifications                     │
│                                                             │
│    Must keep working: Auth, Core business logic            │
└────────────────────────────────────────────────────────────┘

2.3 Test-Then-Refactor Protocol

For modules with poor coverage:

┌─────────────────────────────────────────────────────────────┐
│  UNSAFE → SAFE REFACTORING                                  │
│                                                             │
│  1. BEFORE: Write tests for current behavior                │
│     - Don't change behavior, just document it               │
│     - Tests should FAIL if behavior changes                 │
│                                                             │
│  2. REFACTOR: Make structural changes                       │
│     - Keep behavior identical                              │
│     - Tests should STILL PASS                              │
│                                                             │
│  3. AFTER: Verify all tests pass                           │
│     - If tests fail, behavior changed                      │
│     - Fix the refactor, not the tests                       │
└─────────────────────────────────────────────────────────────┘

Phase 3: Refactoring Execution

3.1 Small Steps Protocol

Rule: Commit after each logical step.

# Step 1: Extract function
git commit -m "refactor: extract validateEmail from processUser"

# Step 2: Move to new module
git commit -m "refactor: move validateEmail to utils/validation"

# Step 3: Update imports
git commit -m "refactor: update imports to use utils/validation"

# Step 4: Clean up
git commit -m "refactor: remove duplicate validation"

Never do multiple refactorings in one commit.

3.2 The Boy Scout Rule

"Leave the code cleaner than you found it."

But only clean what you came to clean. Don't get distracted by other issues.

Phase 4: Verification

4.1 Pre-Commit Checklist

SAFE REFACTOR CHECKLIST
=======================

PRE-REFACTOR
□ Understand why you're refactoring
□ Identify blast radius
□ Ensure tests exist for critical paths
□ Coverage is acceptable (or tests added)
□ Define success criteria

DURING REFACTOR
□ Behavior unchanged (tests pass throughout)
□ Small steps, one logical change at a time
□ Tests still pass after each step
□ No shortcuts or workarounds added

POST-REFACTOR
□ All tests pass
□ Coverage maintained or improved
□ No new code smells introduced
□ Documentation updated (if needed)
□ Peer review (if high-risk)

4.2 Behavior Verification

Run these to confirm behavior is preserved:

# Unit tests
npm test

# E2E tests (if available)
npm run test:e2e

# Manual smoke tests
- Login flow works
- Core feature works
- Error handling works

Risk-Based Refactoring Strategy

Low Risk (Self-Refactor)

Strategy: Refactor with care, verify with tests.

Medium Risk (Peer Review)

Strategy: Self-refactor + quick peer review before merge.

High Risk (Must Have Review)

Strategy: Pair programming or detailed review required.

Common Scenarios

Scenario 1: "I want to rename this function"

Analysis:
- Function used in 15 files
- Medium risk

Steps:
1. [ ] Find all usages (grep)
2. [ ] Write test that calls the function (if none exists)
3. [ ] Rename the function
4. [ ] Update all references
5. [ ] Run tests
6. [ ] Commit

Scenario 2: "This component is too large, I want to split it"

Analysis:
- Single component, 500 lines
- Hooks state management
- High risk

Steps:
1. [ ] Identify logical sections (useEffect, handlers, render)
2. [ ] Write tests for the component
3. [ ] Extract one logical piece at a time
4. [ ] Create child component
5. [ ] Move related state/logic to child
6. [ ] Verify parent still works
7. [ ] Repeat until done

Scenario 3: "I want to change this shared utility"

Analysis:
- Shared by 20+ files
- Low test coverage (30%)
- HIGH RISK

Steps:
1. [ ] MUST increase test coverage first
2. [ ] Write tests for all known use cases
3. [ ] Consider if change is truly necessary
4. [ ] If yes, make smallest possible change
5. [ ] Update all consumers
6. [ ] Run full test suite
7. [ ] Mandatory peer review

Key Principles

1. Tests Are the Contract

If you don't have tests, you can't refactor safely. Tests prove behavior is preserved.

2. Small Commits, Small Risk

The smaller the change, the easier to verify. Large refactors are just many small ones queued up.

3. If It's Hard to Test, It's Hard to Refactor

Difficult-to-test code usually has design problems. Fix the design, then refactor.

4. Don't Mix Refactoring with Feature Work

Separate commits for refactoring and feature changes. This makes rollback easier and review clearer.

5. When in Doubt, Add More Tests

The cost of tests is low. The cost of breaking production is high.

Relationship to Other Skills

• refactor — The refactoring judgment this builds upon
• doublecheck — Verification patterns
• test-think — Test coverage decisions
• pre-commit-review — Pre-commit verification
• debug-session — If something goes wrong during refactor