Testing against a non-controllable stream X-machine using state counting

摘要

Stream X-machines are a form of extended finite state machines that has received extensive study in recent years. A stream X-machine describes a system as a finite set of states, an internal store, called memory, and a finite number of transitions between the states, labelled by function names (the processing functions). One of the great benefits of using a stream X-machine to specify a system is its associated testing method. Under certain design for test conditions, this method produces a test suite that can determine the correctness of the implementation, provided that the processing functions of the stream X-machine specification have been correctly implemented (this can be checked by a separate testing process, using the same method or alternative functional methods). However, the application of the stream X-machine based testing method is often encumbered by the restrictive design for test conditions required. In practical applications, these conditions are achieved by designing extra functionality that will have to be disabled after testing has been completed. This is a time consuming process and can often be a source of error. This paper provides a strong generalisation of the existing method, which requires much laxer design for test conditions; these are naturally satisfied in practical applications and, furthermore, can be introduced into any stream X-machine specification without the need to add extra functionality. Consequently, the generalised method can be applied to virtually any system that can be specified by a stream X-machine.