Offline commissioning testing of HV & EHV cable systems, according to IEC 60840 and 62067 and using Near Power Frequency Resonant Test Sets has been common since the mid 1990s. Recently, similar methodologies have been applied for condition assessment of field-aged HV and EHV cable systems, including mixed cable systems of XLPE and fluid-filled as well as XLPE terminating into GIS. This presentation outlines practices for commissioning and for maintenance of HV & EHV cable systems and discusses avoiding false positive and false negative test outcomes as well as limiting factors related to maintenance tests on older cable systems. Finally, it will touch upon commissioning testing of offshore HV array cable systems.