Software Architect's Handbook

Making small, incremental changes

When refactoring a legacy application, some of the changes that you want to make may be large ones. However, keep in mind that in order to improve a legacy application, the changes do not have to be large and they do not have to be made all at once. Refactoring a legacy application can take time. Small, incremental changes can sometimes be the best approach to improving a legacy codebase. Write and execute unit tests to go along with your changes to ensure that your modifications do not have unintended consequences. With each refactoring, we want to leave the code better than it was before, without changing any of the functionality.

You and your development team may not even be granted time to make improvements. ...