Synchronizing heuristics: Speeding up the fastest

Abstract

Testing is the most expensive and time consuming phase in the development of complex systems. Model–based testing is an approach that can be used to automate the generation of high quality test suites, which is the most challenging part of testing. Formal models, such as finite state machines or automata, have been used as specifications from which the test suites can be automatically generated. The tests are applied after the system is synchronized to a particular state, which can be accomplished by using a synchronizing word. Computing a shortest synchronizing word is of interest for practical purposes, e.g. for a shorter testing time. However, computing a shortest synchronizing word is an NP–hard problem. Therefore, heuristics are used to compute short synchronizing words. Greedy and Cycle are the fastest synchronizing heuristics currently known. In this paper, without sacrificing the quality of the synchronizing words, we improve the time performance of Greedy and Cycle, by restructuring the algorithms and applying some optimizations. Our experimental results show that depending on the automata size, Cycle and Greedy can be made 25 × and 95 × faster, respectively. The suggested improvements become more effective as the size of the automaton increases.