The object model is a very popular paradigm for building distributed applications. Several standardisation efforts are underway that define architectures for distributed computing based on the object model. With object-based service specifications the need for conformance testing of object implementations arises to ensure that objects act as intended. The issue of conformance testing is of particular importance in distributed systems where objects from different sources and manufacturers have to interwork. We discuss the requirements of object conformance testing and the relationship to established protocol conformance testing methodology. For OMG CORBA objects, we propose a test architecture and explain the development of test cases using the standardised test notation TTCN.