Test everything that could possibly break. What does this mean? How is it possible?
In XP, programmers write unit tests for all their code. The rule is: Test everything that could possibly break.
Sometimes people get really angry at us when we talk about this rule. "Don't you know it's impossible to prove that a program works by testing," they'll shout. "Don't you know an infinite number of things could go wrong?"
Yes, your authors took those courses and read those papers, too. Hold your horses, as people used to say in Jeffries's day, and hear us out.
First of all, like all the XP rules, this ...