This paper presents a Scenario Based Testing approach for UML/OCL behavioral models. Scenarios are expressed using a regular expression syntax, that makes it possible to specify iterations and choices between sequences of operation calls, specific operation behaviors to be activated, and intermediate states that have to be reached by the scenario. This expressive scenario language describes sequences of operations that compose the scenario and restrict the execution of the model to representative subset that complements the functional test cases produced by a test generator. This approach is tool supported by a scenario editor and coupled with the model animation engine of the Test Designer tool that is used to animate unfolded test cases and check their consistency with respect to the initial test scenario. The resulting abstract test cases can then be integrated back to the Test Designer repository so as to benefit from the test publishers offered by the tool.