Michael C. Feathers

Legacy code, in Michael Feathers's definition, is simply code without tests, and Working Effectively with Legacy Code, published by Prentice Hall in 2004, is the manual for what to do about it. Feathers built the book from material he had developed for seminars run while consulting at Object Mentor. Two of its terms have since passed into ordinary programming vocabulary: the seam, a place where behaviour can be altered without editing at that spot, and the characterization test, an assertion written to pin down what existing code actually does rather than what someone intended it to do. He went on to serve as chief scientist at Obtiva and founded R7K Research and Conveyance, a consultancy in software and organisation design, and he speaks often at conferences.