Like any software artifact, conceptual schemas of information systems can be tested. Testing conceptual schemas has some similarities with testing programs, but there are important differences. We present a list of six kinds of tests that can be applied to conceptual schemas. Some of them require schemas comprising both the structural and the behavioral parts, but we show that it is useful to test incomplete schema fragments, even if they consist of only a few entity and relationship types, integrity constraints and derivation rules. We present CSTL, a language for writing automated tests of executable schemas written in UML/OCL. CSTL follows the style of the modern xUnit testing frameworks. Tests written in CSTL can be executed as many times as needed. We describe an implementation of a test processor, which includes a test manager and a test interpreter that coordinates the execution of the tests. Finally, we apply CSTL to the conceptual schema of a real-world information system.