Using a typical system test application for distributed robots operating in a joint mission for illustration, the SCenario Specification Language SCSL is introduced. The design of the SCSL is motivated by the fact that according to the current state of the art, highly complex systems are no longer specified by comprehensive, monolithic models. Instead, relevant behaviours are represented separately in parameterised scenarios, and the overall system behaviour is derived from the library containing the complete scenario collection. For the specification of system tests, the scenario-based approach is particularly attractive, since only the test-specific behaviours need to be modelled, so that a comprehensive monolithic model is not needed. SCSL syntax and semantics are explained by means of a system test example for robots performing a salvage mission, and we sketch the tools for automated test data generation, test execution, and test evaluation.