This paper describes the language LUSTRE which is a data flow synchronous language, designed for programming reactive systems-uch as automatic control and monitoring s y s t e m s a s well as for describing hardware. The data flow aspect of LUSTRE makes it very close to usual description tools in these domains (blockdiagrams, networks of operators, dynamical sample-systems, etc.), and its synchronous interpretation makes it well suited for handling time in programs. Moreover, this synchronous interpretation allows it to be compiled into an efficient sequential program. Finally, the LUSTRE formalism is very similar to temporal logics. This allows the language to be used for both writing programs and expressing program properties, which results in an original program verification methodology.

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This paper addresses the problem of automatizing the production of test sequences for reactive systems. We particularly focus on two points: (1) generating relevant inputs, with respect to some knowledge about the environment in which the system is intended to run; (2) checking the correctness of the test results, according to the expected behavior of the system. We propose to use synchronous observers to express both the relevance and the correctness of the test sequences. In particular, the relevance observer is used to randomly choose inputs satisfying temporal assumptions about the environment. These assumptions may involve both Boolean and linear numerical constraints. A prototype tool, called LURETTE, has been developed and experimented, which works on observers written in the LUSTRE programming language.