Distributed Testing of Concurrent Systems: Vector Clocks to the Rescue

The ioco relation has become a standard in model-based conformance testing. The co-ioco conformance relation is an extension of this relation to concurrent systems specified with true-concurrency models. This relation assumes a global control and observation of the system under test, which is not usually realistic in the case of physically distributed systems. Such systems can be partially observed at each of their points of control and observation by the sequences of inputs and outputs exchanged with their environment. Unfortunately, in general, global observation cannot be reconstructed from local ones, so global conformance cannot be decided with local tests. We propose to append time stamps to the observable actions of the system under test in order to regain global conformance from local testing.