This could be a classic example of why unit tests (or at least striving for coverage alone and not functionality) is not good enough. What the pseudo code might

This could be a classic example of why unit tests (or at least striving for coverage alone and not functionality) is not good enough. What the pseudo code might have looked like: def getReleaseDate() = getStartDate() + (getTotalSentencedDays() * getGoodBehaviorCoefficient()) And say all of those functions were covered 100%, then they get the new state supreme court decision changing the contents of "getTotalSentencedDays" and even wrote new tests to make sure it included the "enhancements" and what not. Coverage 100%, unit tests appear to be in order, all done. There was no "testGetReleaseDateWithGoodBehaviorNotAppliedToEnhancements". Hard to catch this stuff when you are close to the code.