title: How to unit test business rules?
body: <p>I need a unit test to make sure I am accumulating vacation hours properly. But vacation hours accumulate according to a business rule, if the rule changes, then the unit test breaks.</p>
  
  <p>Is this acceptable? Should I expose the rule through a method and then call that method from both my code and my test to ensure that the unit test isn't so fragile?</p>
  
  <p>My question is: What is the right way to unit test business rules that may change?</p>