RapidCheck is a C++ framework for property based testing inspired by QuickCheck and other similar frameworks. In property based testing, you state facts about your code that given certain precondition should always be true. RapidCheck then generates random test data to try and find a case for which the property doesn't hold. If such a case is found, RapidCheck tries to find the smallest case (for some definition of smallest) for which the property is still false and then displays this as a counterexample. For example, if the input is an integer, RapidCheck tries to find the smallest integer for which the property is false.