Software Test Libraries (STLs) are used to test digital circuits during manu- facturing and in-field diagnostics. An STL is a set of test routines that runs on the target system to stimulate the circuit and check its behavior. In many products, STLs run in short idle windows, for example between normal tasks, so they must finish quickly. They must also fit within tight memory limits, since the test code and its data share limited resources with the application. In practice, an STL must reach high fault coverage, but it also must run fast and fit in memory, so it can execute during short idle times without a!ecting normal operation.