refactor-with-safety

To refactor code without breaking existing behavior, write characterization tests to lock in current outputs, then implement small, incremental changes with isolated commits while running the full test suite after each step to verify behavior is preserved.

Characterization tests capture and lock in the current observable behavior of your code before you change it. You need them during a code refactor to ensure that improving clarity, reducing duplication, or modernizing APIs does not alter external outputs.

The best way to plan incremental refactoring steps is to create a specific plan for each change, implement modifications one isolated commit at a time, and execute full test suite verification after every step to guarantee observable behavior remains unchanged.

Yes, you can rename identifiers and modernize APIs while preserving test coverage by establishing baseline characterization tests first, then applying the changes through small, verifiable incremental steps with full test suite verification.

Incremental refactoring works for reducing code duplication across any software project by enforcing small commit steps, a dedicated plan per change, and continuous test suite verification to maintain observable behavior throughout the cleanup process.