A Rigorous Method for Testing Real-Time Reactive Systems

Real-time reactive systems are complex systems to design and verify. Rigorous testing of realtime reactive systems complement the more difficult and expensive formal verification process. This paper gives a rigorous method for black-box testing of real-time reactive systems whose design specifications are given in the Timed Reactive Object Model (TROM) formalism. 1 Introdu tion This paper discusses a black-box testing method for real-time reactive systems. Black-box testing relies on the specification of the system under test, and generates test cases from the specification to test the conformance of the implementation with respect to the system specification. Usually the results obtained from an implementation are compared with the oracle and the correctness of the implementation is certified only when they match for all test cases. When a formal specification of the system is available, it can be used both as an oracle and a medium to generate test cases. The term reactive was introduced by Harel and Pnueli [12] to designate systems that continuously interact with their environment and to distinguish them from interactive and transformational systems. Two important properties characterize reactive systems: stimulus synchronization: the process always reacts to a stimulus from its environment; response synchronization: the time elapsed between a stimulus and its response is acceptable to the relative dynamics of the environment, so that the environment is still receptive to the response. When the behavior of the reactive system is regulated by time, the system is called a real-time reactive system. Examples of such systems include patient monitoring systems, watchdogs for nuclear power plants, and air traffic control systems. In the context of real-time reactive systems, which are mostly safety-critical, the consequences of failure are extremely high, such systems are expected to perform as desired and never fail. Therefore, verification and testing must be conducted right from the early stages of specification and design to ensure correct implementation of safety and time-dependent behavior. A mechanical verification approach for reactive systems, proposed by Muthiayen and Alagar [15], complements the testing method discussed in this paper. This work is supported by grants from Natural Sciences and Engineering Research Council, Canada, and Concordia University Graduate Fellowship.