How does the skill ensure refactoring doesn't break existing features?

It mandates a 'Safety First' approach, requiring version control and the creation of E2E or 'Golden Master' tests before any structural code changes are made.

What is the Humble Object pattern mentioned in the guide?

It is a design pattern used to make hard-to-test objects (like those tied to UI or external APIs) testable by extracting their logic into a separate, decoupled class.

What does this skill consider to be 'legacy code'?

Following Michael Feathers' definition, this skill treats any code without automated tests as legacy code, regardless of when it was written.

Can I use this for any programming language?

Yes, the principles of TDD, Seams, and Clean Architecture provided by this skill are architectural patterns applicable to almost any modern programming language.

Does this skill help with Domain-Driven Design (DDD)?

Yes, Phase 3 specifically focuses on Extracting Domain Models to separate business logic from infrastructure and framework concerns.

Legacy Code Improvement Guide

Name: Legacy Code Improvement Guide
Author: kazuph

bykazuph

•

Security & Testing

Transforms untested legacy code into maintainable, structured systems through a guided five-phase refactoring framework.

Based on the renowned methodologies of Takuto Wada and Michael Feathers, this skill provides a systematic approach to modernizing 'legacy code'—defined primarily as code without tests. It guides developers through the critical journey of securing code with version control, implementing initial E2E tests to create a safety net, and identifying 'seams' to isolate dependencies. By applying patterns like Humble Object, TDD, and Domain Model extraction, it helps transition monolithic or 'Smart UI' codebases into clean, decoupled architectures that are easy to test and extend.

Key Features

01Transition tactics for moving from stateful variables to fact-based state calculation

02Identification of 'Seams' to isolate hard-to-test dependencies like APIs and random values

03Strategies for Golden Master testing to ensure functional parity during refactoring

04Step-by-step guidance from initial Git commit to Clean Architecture implementation

0515 GitHub stars

06Humble Object pattern implementation to separate logic from framework-specific code

Use Cases

01Decoupling business logic from frameworks to enable faster unit testing and better maintainability

02Safely adding new features to inherited codebases with zero existing test coverage

03Refactoring monolithic AWS Lambda or Express handlers into testable domain models

What are Skills?·How to Install

Install with 🐟 Skill.Fish

npx skillfish add kazuph/dotfiles improve-legacy-code

For use in Claude.ai and ChatGPT

Download Skill