We introduce eCAT, a tool that supports deriving test cases semi-automatically from goal-based analysis diagrams, generates meaningful test inputs based on agent interaction ontology, and more importantly it can evolve and execute test cases automatically and continuously on a multi-agent system (MAS). Our experiments have shown that the proposed tool can exercise MAS more extensively and effectively than manual testing under the usual time constraints. Categories and Subject Descriptors D.2.5 [Software Engineering]: Testing and Debugging General Terms Verification Keywords Testing tools, multi-agent systems