Introduction of time dependencies in usage model based testing of complex systems

Model-driven testing based on Markov chain usage models (MCUM) is an established method to address testing issues. It is not possible, however, to describe by means of MCUMs the timing of stimuli and time dependencies between inputs and outputs of a system. Additional concepts and information is needed. In this paper it is presented how Timed Usage Models (TUM) can be used to solve this issue. Concepts for stimuli and responses are introduced, that comprise that something must happen before a time interval, after a time interval or within a time interval. It is presented how this can be described by TUMs. TUMs are enhanced MCUMs that allow the usage of distributions of time. The computations for TUMs are based on semi-Markov processes and are therefore not restricted to discrete steps in time. Therefore, indicators and metrics for the test planning and management can be derived that take into account time. Test cases can be derived that reflect variability in inputs and, additionally, variability in timing of inputs. Complex real time systems require a test method that provides the possibility to handle the effect of timing and variability in timing of inputs to the system.