XP Values

Besides simplicity, Design by Contract also affects the three other values of XP: communication, feedback, and courage. Communication is increased by the documentation effect of contracts, as explained earlier. Feedback is increased by providing developers with early notice of interface misuse, when contract checking is switched on during test runs.

Concerning courage, developers often hesitate to change or refactor their own code when it is using or providing external interfaces, because they fear breaking them. Contracts are a safeguard against breaking interfaces and therefore encourage programmers to make the necessary changes.