 This is usually done through the use of perturbation functions which are simple functions which take an existing value and perturb it via some logic into another value, for example

In this case pFunc is the perturbation function and it is applied to the return value of the function that has been called introducing a fault into the system.Runtime Injection techniques use a software trigger to inject a fault into a running software system.Faults can be injected via a number of physical methods and triggers can be implemented in a number of ways, such as