Refactoring Legacy Code

Overview

Big-bang rewrites fail. Refactoring without tests creates new bugs. Scope creep turns a "quick cleanup" into a six-month project.

Core principle: ALWAYS write characterization tests before changing legacy code. Understand current behavior before changing it.

Violating the letter of this process is violating the spirit of refactoring.

The Iron Law

NO REFACTORING WITHOUT CHARACTERIZATION TESTS FIRST

If you haven't captured existing behavior in tests, you cannot change the code.