I have a test system but frankly I purchased it for other needs (Kind of expensive) but the unit performs multiple functions.. One is Spike supression and if it's more than 5 years old odds are that's not as good as it once was.. However you can easily add mnore spike supression.. (the devices providing are even easy to replace)
The other functions are power line monitoring and high/low voltage cutoff. If hte LCD display is showing the voltage and current. then the monitoring is likely working. To test current requires a variable AC voltage source.. I have a small one (Good enough for testing) but odds are if the display displays the proper voltage plus or minus one volt (Compare to meter) then it's working.