In this paper, we analyze the use of UML as a starting point to go from design issues to end of production testing of complex embedded systems. The first point is the analysis of the big gap between system signals and UML messages; then the paper focuses on the additional information necessary to fill such gap; different test types are considered, focusing on the application software test; finally the actuation and observation are both analyzed inside the test environment, with particular care to the black -box requirement for behavioral testing. The emphasis of the work is on the resulting test engine definition, verified on a complex case study of a top-of-the- line automotive application; this application is a modern car console, grouping many controls of car-related devices, such as phone, navigation, radio, CD. The testing of GSM capabilities of such device is studied in particular.