결함비용증가
XP에서 테스트의 비용효과성을 높이기 위한 두 가지 원칙 중 하나:
Defect Cost Increase (DCI) is the second principle applied in XP to increase the cost-effectiveness of testing. DCI is one of the few empirically verified truths about software development: the sooner you find a defect, the cheaper it is to fix. If you find a defect after a decade of deployment you’ll have to reconstruct a lot of history and context to figure out what the code was supposed to do in the first place, which of those assumptions are in error, and what should be fixed so the rest of the (presumably correct) program remains undisturbed. Catch the same defect the minute it is created and the cost to fix it will be minimal. …
DCI tells us to put testing near coding, but it doesn’t say exactly when to test. Testing after implementation has the advantage that it makes sense. After all, you can’t check the tolerances of a physical part you haven’t yet made. This is where the physical metaphor behind the word “testing” is misleading. Because software is a virtual world, “testing” before or after makes equal sense. You can write code to fit a mold or a mold to fit code. You can do whichever creates the most benefit. In the end you put two together and see if they match. —p98-101, Extreme programming explained