1. A method in a computing system for augmenting software, comprising: receiving in a target computer system an augmentation specification specifying (a) a function to be augmented, the specified function being among software executed in the computing system, (b) a parameter of the function to be tested, (c) a test to apply to the specified parameter, and (d) a modification to perform to the behavior of the function if the specified test is not satisfied by the specified parameter; and when the specified function is invoked on the target computer system, if the specified test is not satisfied by the specified parameter, performing the specified modification to the behavior of the specified function.