Operating systems (OS) are increasingly geared towards support of diverse peripheral components, both hardware (HW) and software (SW), rather than explicitly focused on increased reliability of delivered OS services. The interface between the OS and the HW devices is provided by device drivers. Furthermore, drivers have become add-on COTS components to support the OS's capabilities of widespread device support. Unfortunately, drivers constitute a major cause of system outages, impacting overall service reliability. Consequently, the testing of drivers becomes important. However, despite the efforts to develop appropriate testing methods, the multitude of possible system configurations and lack of detailed OS specifications makes the task difficult. Not requiring access to OS source code, this paper develops novel, non-intrusive support for test methods, based on ascertaining test progress from a driver's operational state model. This approach complements existing schemes, enhancing the level of accuracy of the test process by providing test location guidance. © Springer-Verlag Berlin Heidelberg 2006.