Interoperability testing is a key validation activity for networked devices that are to function as part of a larger distributed system. In this paper we describe an approach for generating interoperability tests for networked media devices based on the Universal Plug and Play (UPnP) AV architecture. Our approach is based on constructing formal models of the various entities as specified in the UPnP AV architecture and composing these to form a complete model for a test set-up (as given by the test engineer) and then generating tests from this complete model based on model coverage and well chosen test purposes. We illustrate this for an example test set-up. The tests that we generate are currently being used at our certification test lab. We believe that this approach can be used for similar testing activities in different domains.