This paper presents a test framework to support unit component testing in distributed component-based systems that are built upon component technologies like CORBA, COM/.NET, J2EE/RMI. The framework exploits automatic code instrumentation at the stubs and the skeletons of the calls in order to monitor a global call session. The calls can be cross-thread, cross-process and cross-processor. We further define certain testing-related interfaces for driver components in the component test harness and extend the IDL compiler, such that at runtime, test-related attributes can be automatically embedded in the call session identifier and propagated system-wide. As a result, various support for unit component testing can be enabled, including behavior coordination for stub components, collaborator component determination from historical execution, selective regression testing, and crash site pinpointing.