[+Bourbon]

Although having a regression suite is certainly a compelling benefit of testing, testing, in my opinion, pertains to more than detecting regressions.

Writing tests:

• gives you immediate feedback about the quality of your design ideas;
  


• encourages you towards code that is both loosely coupled and highly cohesive;
  


• adds an executable specification of the what the code should do; and,
  


• lets you know when you've done enough, discouraging gold plating and from adding functionality until deemed necessary (because YAGNI!).