System for simulating one or more sub-systems of a tested
system includes: (a) a
sequence diagram storage and engine unit containing a predefined
sequence diagram defining the intercommunication of messages between the various sub-systems of a real
system in terms of at least time, message name, issuing sub-
system, and destination sub-system. An indicator indicates to said
sequence diagram storage and engine unit, those missing sub-systems, which have to be simulated. A
receiver within said sequence diagram storage and engine unit receives an activation
signal for the sequence diagram, and for eliminating all those messages in the sequence diagram relating to non-missing sub-systems, while maintaining those messages relating to missing sub-systems. One or more simulated sub-system units, each contain
a domain of predefined output messages in appropriate format that can be issued by the simulated sub-system unit, and predefined input messages in appropriate format that can be received by the simulated sub-system unit, both domains being essentially identical to those of the corresponding real sub-systems of the system. A real time engine activates the sequence diagram, for receiving messages relating to missing sub-systems from one or more of the simulated sub-systems units, for introducing in real time the received messages on a
bus leading to the real sub-systems, and for receiving messages issued by the real sub-systems and conveying them in real time to the simulated sub-system units.