OpenClosedPrinciple

In XP terms this would imply that you can add new tests but you cannot break old ones.

This leads me to the first conclusion that the OpenClosedPrinciple does not work with XP because you may need to refactor out functionality to a new class, breaking the tests until you also refactor them.

This leads on to a prediction. In an XP system some classes will evolve to 'closure', that is to say that they will stabilise and cease to be refactored.

Has anybody observed this yet?

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No. Refactoring is how you move stable, generic code into "closed" packages. Most people find you can't just sit down and write systems with different abstraction layers (see DependencyInversionPrinciple? by ObjectMentor -- try WikiWikiWeb?): they evolve by refactoring, so the two go hand in hand.

--TomAyerst ³³agent³Mozilla/4.0 (compatible; MSIE 5.0; Windows NT; DigExt?; UKPORTAL)³OpenClosedPrinciple