This paper describes our experiences with integrating and testing an embedded, system-wide feature called Dynamic Voltage and Frequency Scaling (DVFS) in a software platform for mobile devices. DVFS affects the whole system by scaling the hardware performance levels during run-time. Implementing and testing the basic functionality of DVFS was easy, however verifying that the whole system worked after integration was more difficult. The platform was legacy code which had not been developed with any consideration for this kind of a feature. We had to consider the complex run-time behaviour of the whole platform, including operating system services, device drivers and applications. DVFS could cause problems and failures in almost any part of the system. Based on our experiences, we describe problems in integrating and testing a system-wide feature like DVFS and suggest possible directions for future research to help address some of these problems.