QA Refactoring Safety
Use this skill to refactor safely: preserve behavior, reduce risk, and keep CI green while improving maintainability and delivery speed.
Defaults: baseline first, smallest safe step next, and proof via tests/contracts/observability instead of intuition.
Quick Start (10 Minutes)
- If key context is missing, ask for: what must not change (invariants), risk level (money/auth/migrations/concurrency), deployment constraints, and the smallest boundary that can be protected by tests.
- Confirm baseline:
maingreen; reproduce the behavior you must preserve. - Choose a boundary: API surface, module boundary, DB boundary, or request handler.
- Add a safety net: characterization/contract/integration tests at that boundary.
- Refactor in micro-steps: one behavior-preserving change per commit/PR chunk.
- Prove: run the smallest relevant suite locally, then full CI; keep failures deterministic.
Core QA (Default)
Safe Refactor Loop (Behavior First)
- Establish baseline: get
maingreen; reproduce the behavior you must preserve. - Define invariants: inputs/outputs, error modes, permissions, data shape, performance budgets.
- Add a safety net: write characterization/contract/integration tests around the boundary you will touch.
- Create seams: introduce injection points/adapters to isolate side effects and external dependencies.
- Refactor in micro-steps: one behavior-preserving change at a time; keep diffs reviewable.
- Prove: run the smallest relevant suite locally, then full CI; keep failures debuggable and deterministic.
- Ship safely: use canary/dark launch/feature flags when refactors touch production-critical paths.
Risk Levels (Choose Safety Net)
| Risk | Examples | Minimum required safety net |
|---|---|---|
| Low | rename, extract method, formatting-only | unit tests + lint/type checks |
| Medium | moving logic across modules, dependency inversion | unit + integration/contract tests at boundary |
| High | auth/permission paths, concurrency, migrations, money/data-loss paths | integration + contract tests, observability checks, canary + rollback plan |
Test Strategy for Refactors
- Prefer contract and integration tests around boundaries to preserve behavior.
- Use snapshots/golden masters only when outputs are stable and reviewed (avoid "approve everything" loops).
- For invariants, consider property-based tests or table-driven cases (inputs, edge cases, error modes).
- Avoid making E2E/UI tests the primary safety net for refactors; keep most safety below the UI.
- For flaky areas: fix determinism first (seeds, time, ordering, network) before trusting results.
CI Economics and Debugging Ergonomics
- Keep refactor PRs small and reviewable; avoid refactor + feature in one PR.
- Require failure artifacts for tests guarding refactors (logs, trace IDs, deterministic seeds, repro steps).
- Reduce diff noise: isolate formatting-only changes (or apply formatting repo-wide once with buy-in).
- Keep
git bisectviable: avoid mixed "mechanical + semantic" changes unless necessary.
Do / Avoid
Do:
- Add missing tests before refactoring high-risk areas.
- Add guardrails (linters, type checks, contract checks, static analysis/security checks) so refactors don't silently break interfaces.
- Prefer "branch by abstraction" / adapters when you need to swap implementations safely.
Avoid:
- Combining large structural refactors with behavior changes.
- Using flaky E2E as the primary safety net for refactors.
Quick Reference
| Task | Tool/Pattern | Command/Approach | When to Use |
|---|---|---|---|
| Long method (>50 lines) | Extract Method | Split into smaller functions | Single method does too much |
| Large class (>300 lines) | Split Class | Create focused single-responsibility classes | God object doing too much |
| Duplicated code | Extract Function/Class | DRY principle | Same logic in multiple places |
| Complex conditionals | Replace Conditional with Polymorphism | Use inheritance/strategy pattern | Switch statements on type |
| Long parameter list | Introduce Parameter Object | Create DTO/config object | Functions with >3 parameters |
| Legacy code modernization | Characterization Tests + Strangler Fig | Write tests first, migrate incrementally | No tests, old codebase |
| Automated quality gates | ESLint, SonarQube, Prettier | npm run lint, CI/CD pipeline | Prevent quality regression |
| Technical debt tracking | SonarQube, CodeClimate | Track trends + hotspots | Prioritize refactoring work |
Decision Tree: Refactoring Strategy
Code issue: [Refactoring Scenario]
├─ Code Smells Detected?
│ ├─ Duplicated code? → Extract method/function
│ ├─ Long method (>50 lines)? → Extract smaller methods
│ ├─ Large class (>300 lines)? → Split into focused classes
│ ├─ Long parameter list? → Parameter object
│ └─ Feature envy? → Move method closer to data
│
├─ Legacy Code (No Tests)?
│ ├─ High risk? → Write characterization tests first
│ ├─ Large rewrite needed? → Strangler Fig (incremental migration)
│ ├─ Unknown behavior? → Characterization tests + small refactors
│ └─ Production system? → Canary deployments + monitoring
│
├─ Quality Standards?
│ ├─ New project? → Setup linter + formatter + quality gates
│ ├─ Existing project? → Add pre-commit hooks + CI checks
│ ├─ Complexity issues? → Set cyclomatic complexity limits (<10)
│ └─ Technical debt? → Track in register, 20% sprint capacityRelated Skills
- Debugging production issues: qa-debugging
- Code review process and checklists: software-code-review
- New architecture design from scratch: software-architecture-design
- Test strategy and coverage planning: qa-testing-strategy
Scope Boundaries (Handoffs)
- Pure test flake cleanup (timers, ordering, retries):
../qa-debugging/SKILL.md - Pure performance tuning (SQL, indexing, query plans):
../data-sql-optimization/SKILL.md - Architecture redesign decisions (service boundaries, eventing):
../software-architecture-design/SKILL.md
Operational Deep Dives
Shared Foundation
- ../software-clean-code-standard/references/clean-code-standard.md - Canonical clean code rules (
CC-*) for citation - Legacy playbook: ../software-clean-code-standard/references/code-quality-operational-playbook.md -
RULE-01–RULE-13, decision trees, and operational procedures - ../software-clean-code-standard/references/refactoring-operational-checklist.md - Refactoring smell-to-action mapping, safe refactoring guardrails
- ../software-clean-code-standard/references/working-effectively-with-legacy-code-operational-checklist.md - Seams, characterization tests, incremental migration patterns
Skill-Specific
See references/operational-patterns.md for detailed refactoring catalogs, automated quality gates, technical debt playbooks, and legacy modernization steps.
Templates
Use copy-paste templates in assets/ for checklists and quality-gate configs:
- Refactoring: assets/process/refactoring-checklist.md, assets/process/code-review-quality.md
- Technical debt: assets/tracking/tech-debt-register.md
- Quality gates: assets/quality-gates/javascript/eslint-config.js, assets/quality-gates/platform-agnostic/sonarqube-setup.md
Resources
Use deep-dive guides in references/ (load only what you need):
- Operational Patterns: references/operational-patterns.md - Core refactoring catalogs, quality gates, and legacy modernization
- Refactoring Catalog: references/refactoring-catalog.md
- Code Smells Guide: references/code-smells-guide.md
- Technical Debt Management: references/tech-debt-management.md
- Legacy Code Modernization: references/legacy-code-strategies.md
- Characterization Testing: references/characterization-testing.md - Golden master and approval testing patterns
- Strangler Fig Migration: references/strangler-fig-migration.md - Incremental legacy migration strategies
- Automated Refactoring Tools: references/automated-refactoring-tools.md - Codemods, AST transforms, and IDE refactoring
Optional: AI / Automation
Do:
- Use AI to propose mechanical refactors (rename/extract/move) only when you can prove behavior preservation via tests and contracts.
- Use AI to summarize diffs and risk hotspots; verify by running targeted characterization tests.
- Prefer tool-assisted refactors (IDE/compiler-aware, codemods) over freeform text edits when available.
Avoid:
- Accepting refactors that change behavior without an explicit requirement and regression tests.
- Letting AI "fix tests" by weakening assertions to make CI green.
See data/sources.json for curated external references.
Fact-Checking
- Use web search/web fetch to verify current external facts, versions, pricing, deadlines, regulations, or platform behavior before final answers.
- Prefer primary sources; report source links and dates for volatile information.
- If web access is unavailable, state the limitation and mark guidance as unverified.