This is what Michael Feathers calls 'seams' in his book, Working With Legacy Code. Often, you have to do exploratory testing, that is, you don't really know the

This is what Michael Feathers calls 'seams' in his book, Working With Legacy Code. Often, you have to do exploratory testing, that is, you don't really know the requirements but you make tests that the current code passes. Then you can refactor it. That way, current code behavior won't be changed. Very good read, if you need to deal with legacy code and you don't know where to start. http://www.amazon.com/Working-Effectively-Legacy-Michael-Feathers/dp/0131177052 http://www.amazon.com/Working-Effectively-Legacy-Michael-Fea...