Online model-based testing is one of the most suitable techniques to assess the proper behavior of service orchestrations. However, the diverse panorama in terms of modeling languages and test case generation tools is a limitation to widespread adoption. We advocate that the application of Model-Driven Engineering principles as meta-modeling and model transformation can cope with this problem, improving the interoperability of artifacts in the test case generation process, thus bringing benefits in case of agile development processes, where system and technology evolution is frequent. In this paper, we present our contribution to this idea, introducing i) a reference metamodel, which stores the business process behavior and the information to generate input models for testing tools, and ii) transformations from orchestration languages towards testing tools. The proposed approach is implemented in a testing framework and evaluated on a case study where multiple orchestrations are expressed in two languages. Also, the paper presents how test cases are appropriately generated and successfully executed, starting from an orchestration model as a consequence of successful transformations.