Legacy Code
Domain: Refactoring
🎯 Motivation
Legacy code is code without tests, often old and feared. Understanding strategies to work with it safely is crucial because most real-world development happens in existing codebases.
📋 Concrete Example
A 15-year-old billing module with no tests and one developer who understands it is legacy code. You add “characterization tests” capturing current behavior before changing anything.
🔗 Analogy
An old house with wiring no one fully understands is legacy. You do not demolish it blindly; you map the circuits first, then renovate room by room with care.