Conceptual schemas are software artifacts and consequently, they can also be tested. Testing conceptual schemas has some similarities with testing software programs but there are also important differences. Our work is addressed to explore the use of testing in the conceptual modeling activity. We developed CSTL (Conceptual Schema Testing Language), a language for writing automated tests of executable conceptual schemas. In this report, we present this language in detail and we show example results of using CSTL to test the conceptual schema of a real-world information system, the osCommerce system.