Having your code tested protects you from making accidental errors. But it also opens up different possibilities. When your code is covered by test cases, you don't have to fear refactoring. Refactoring is the process of transforming code that does its job into code that is functionally similar, except it has better internal organization. You may be wondering why you need to change the code's organization. There are several reasons for this.
First of all, your code may no longer be readable, which means every modification takes too much time. Second, fixing a bug you are about to fix will make some other features behave incorrectly as the code gathered too many workarounds and special cases over time. Both of those reasons can be summed up as productivity improvements. They will make maintenance cheaper in the long run.
But apart from productivity, you may also want to improve performance. This can mean either runtime performance (how the...
