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: main green; 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 main green; 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 bisect viable: 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 capacity

Related 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.