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:<p><pre><code>    def getReleaseDate() = getStartDate() + (getTotalSentencedDays() * getGoodBehaviorCoefficient())
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And say all of those functions were covered 100%, then they get the new state supreme court decision changing the contents of &quot;getTotalSentencedDays&quot; and even wrote new tests to make sure it included the &quot;enhancements&quot; and what not. Coverage 100%, unit tests appear to be in order, all done. There was no &quot;testGetReleaseDateWithGoodBehaviorNotAppliedToEnhancements&quot;. Hard to catch this stuff when you are close to the code.