This paper investigates software agents testing, and in particular how to automate test generation. We propose a novel approach, which takes advantage of agent interaction ontologies that define content semantic of agent interactions to: (i) generate test inputs; (ii) guide the exploration of the input space during generation; and, (iii) verify messages exchanged among agents with respect to the defined interaction ontology. We integrated the proposed approach into a testing framework, called eCAT, which can generate and evolve test cases automatically, and run them continuously. Categories and Subject Descriptors D.2.5 [Software Engineering]: Testing and Debugging General Terms Verification Keywords Ontology-based test generation