Exploration Through Example

Example-driven development, Agile testing, context-driven testing, Agile programming, Ruby, and other things of interest to Brian Marick

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Tue, 18 Jul 2006

Refactoring, defined

A while back, I sat in while Ralph Johnson gave a dry run of his ECOOP keynote. Part of it was about refactoring: behavior-preserving transformations. The call was for research on behavior-changing transformation that are like refactorings: well-understood, carefully applied, controlled.

Ralph mentioned that persistent question: what does "behavior-preserving" mean? A refactoring will change memory consumption, probably have a detectable effect on speed, etc.

My reaction to that, as usual, was that a refactoring preserves behavior you care about. Then I thought, well, you should have a test for behavior you care about. ("If it's not tested, it doesn't work.") That, then, is my new definition of refactoring:

A refactoring is a test-preserving transformation.

If you care about performance, a refactoring shouldn't make your performance tests fail.

## Posted at 21:30 in category /coding [permalink] [top]