On top of biennial transponder, altimeter and altitude reporting certifications
PDG Services also has line testing capabilities for the following;
With digital multi-meters, milli-ohm meters, meg-ohm meters, AC/DC amp meter, watt meters, function generators, frequency counters, and even a magnetometer, there aren't too many problems that can not be figured out, especially if there are prints. (Sorry, I do not have any ghost chasers)
Did I mention installations?