Real-time operating systems (RTOS) are becoming quite common in embedded applications and its correct operation is crucial to ensure system quality and reliability. However, the test of this specialized software has been often neglected in the embedded software testing literature. This paper presents preliminary results on the testing of the exception handling routines in an embedded operating system (EOS). We first analyze what makes an EOS so difficult to test. Then, we present some experiments that will help to devise a test methodology for this specific software.