The Flow of Refactoring
In a Test-First context, refactoring has the same flow as any other code change. You have your automated tests. You begin the refactoring by making the smallest discrete change you can that will compile, run, and function. Wherever possible, you make such changes by adding to the existing code, in parallel with it. You run the tests. You then make the next small discrete change, and run the tests again. When the refactoring is in place and the tests all run clean, you go back and remove the old smelly parallel code. Once the tests run clean after that, you are done.
Refactoring Automation in IDEs
Refactoring is much, much easier to do automatically than it is to do by hand. Fortunately, more and more Integrated Development Environments (IDEs) are building in automated refactoring support. For example, one popular IDE for Java is eclipse, which includes more auto-refactorings all the time. Another favorite is IntelliJ IDEA, which has historically included even more refactorings. In the .NET world, there are at least two refactoring tool plugins for Visual Studio 2003, and we are told that future versions of Visual Studio will have built-in refactoring support.
To refactor code in eclipse or IDEA, you select the code you want to refactor, pull down the specific refactoring you need from a menu, and the IDE does the rest of the hard work. You are prompted appropriately by dialog boxes for new names for things that need naming, and for similar input. You can then immediately rerun your tests to make sure that the change didn’t break anything. If anything was broken, you can easily undo the refactoring and investigate.