No need to test anything, just look at what kind of service is installed and it's amperage. You can bring an electrician and not reveal that it's for a mining operation, you know? He doesn't give a fuck why he's there, as long as he's getting paid.
Agreed - I would have one come out to inspect the panel / mains for aged breakers or crappy wiring before anything was brought to the warehouse.
Run all the circuits/outlets yourself for whatever racking setup you do and take head of your amperage per circuit and you should be fine...
but, that's just my 2 cents... meh