Taming Legacy Code: A Summary of Michael Feathers' "Working Effectively with Legacy Code"

This article summarizes the core ideas of Michael Feathers' classic book, "Working Effectively with Legacy Code." The book argues that the crux of legacy code is the lack of tests. To safely modify legacy code, tests must be added first. This is challenging because adding tests requires modifying the code, creating a paradox. The book outlines steps for identifying change points (Seams), breaking dependencies, writing tests, and refactoring, along with incremental testing techniques (Sprout and Wrap) and a technique to quickly understand code (Scratch Refactoring). The author emphasizes the importance of unit tests and introduces characterization tests to capture the existing code's behavior. Finally, the article advises avoiding direct dependency on library implementations to reduce maintenance costs.