# Nikoheikkila Agents Tdd Refactor > TDD Refactor Phase - Improve Code Quality and Design - Skill: `tomevault-io/nikoheikkila-agents-tdd-refactor` (Agent Skill, multi-file: 2 files) - Install (CLI): `npx skillmds@latest add tomevault-io/nikoheikkila-agents-tdd-refactor` - Raw SKILL.md: https://api.skillmd.com/api/skills/tomevault-io/nikoheikkila-agents-tdd-refactor/raw - Safety review: pending (external: skill-scanner PASS, skillspector PASS) - Works with: Claude Code, Claude.ai, OpenAI Codex - Category: Coding & Dev Tools - Author: tomevault-io (https://skillmd.com/u/tomevault-io) - Updated: 2026-09-17 - Page: https://skillmd.com/skills/tomevault-io/nikoheikkila-agents-tdd-refactor --- # TDD Refactor Phase - Improve Code Quality and Design ## Quality Gates - **Definition of Done adherence** - Ensure all tests are passing by running all tests before starting any activity. - **Code smells** - Identify and eliminate code smells such as duplicated code, long methods, large classes, and complex conditionals. - **Security requirements** - Address any security considerations. - **Performance criteria** - Meet any performance requirements. ## Core Principles ### Code Quality Improvements - **Remove duplication** - Extract common code into reusable classes and methods. Follow the "Rule of Three" meaning knowledge should be abstracted only after it has been used in three places. - **Improve readability** - Use intention-revealing names and clear structure aligned with the domain. - **Apply SOLID principles** - **Single Responsibility Principle** - Ensure each class and method has one and only one reason to change. - **Open/Closed Principle** - Make code open for extension but closed for modification. - **Liskov Substitution Principle** - Subtypes must be substitutable for their base types. - **Interface Segregation Principle** - Use specific abstract classes rather than general ones. - **Dependency Inversion Principle** - Depend on abstractions, not concrete implementations. - **Simplify complexity** - Break down large methods, reduce cognitive and cyclomatic complexities. ### Design Excellence - **Class length** - Keep the length of classes under 100 lines. - **Method length** - Keep the length of methods under 10 lines. - **Composition over inheritance** - Prefer writing small focused classes and compose behaviour from them. - **Dependency injection** - Use dependency injection through class constructor arguments. - **Modularization** - Organize code into coherent modules and packages. - **Pydantic models** - Leverage Pydantic for configuration objects, data, and domain models. ### Test Quality - **Fast tests** - Ensure tests remain fast and isolated. - **Coverage maintenance** - Test coverage must not decrease during refactoring. ### Safe Refactoring Patterns Use battle-tested refactoring techniques: - **Extract Constant** - Move magic numbers and strings to named constants. - **Extract Method** - Break down long methods into smaller ones. - **Extract Class** - Split large classes with multiple responsibilities. - **Rename** - Use intention-revealing names for variables, methods, and classes. - **Inline Variable/Method** - Simplify code by removing unnecessary indirection. - **Move Method/Field** - Relocate code to more appropriate locations. - **Replace Conditional with Polymorphism** - Use objects instead of complex conditionals. ### Documentation - **Update documentation** - Revise inline comments and docstrings to match refactored code. Ensure the documentation always answers to question WHY instead of WHAT. - **Record decisions** - Document non-obvious design decisions made during refactoring. ### Performance & Quality Validation - **Avoid premature optimization** - Only optimize when there are actual performance issues. - **Remove dead code** - Eliminate unused imports, variables, and unreachable code. - **Run static analysis** - Use linters and type checkers to catch issues early. ## Execution Guidelines 1. **Ensure green tests** - All tests must pass before refactoring can start. Verify this by running all tests. 2. **Small incremental changes** - Refactor in tiny, atomic steps. 3. **Apply one improvement at a time** - Focus on a single refactoring technique. 4. **No test code modifications** - Do NOT modify any test code during refactoring. 5. **Continuous testing** - Run tests after EACH and EVERY change. 6. **Coverage preservation** - Ensure test coverage doesn't decrease during refactoring. 7. **Static analysis** - Run linters and static analysis tools after changes. 8. **API stability** - Validate that publicly exposed APIs and contracts remain unchanged. 9. **Rollback readiness** - Revert to a previous working state when tests become unstable or complexity increases to the point you cannot reason about the changes. ## Refactor Phase Checklist ### Before Starting - [ ] All tests pass before starting. - [ ] Current test coverage recorded. ### During Refactoring - [ ] Linters and static analysis tools run successfully. - [ ] Tests pass after every change. - [ ] Specific refactoring technique documented. - [ ] No modifications made to test code. ### After Refactoring - [ ] Code readability and design improved. - [ ] All tests remain green. - [ ] Test coverage is maintained or improved. - [ ] Public APIs and contracts unchanged. - [ ] Unused code removed (imports, variables, dead code). - [ ] Documentation updated (comments, docstrings). - [ ] Performance improved where applicable. ### Technical Debt - [ ] Remaining refactoring opportunities documented and suggested to the user. - [ ] Non-obvious design decisions recorded. - [ ] Breaking changes or impacts flagged. --- > Converted and distributed by [TomeVault](https://tomevault.io/claim/nikoheikkila) — claim your Tome and manage your conversions.