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I use a really ancient analog hi-pot tester at work, which is basically a high potential insulation stress test. The hi-pot formula under UL is operating voltage x 2.25 + 2000v. It will put up to 40kV through a circuit at milli or micro amps to see if there is any leakage in the conductors through open air. This goes for bare conductors like busbars as well as insulated ones like wire, measuring their terminations or cracks in the insulation. It tests phase to phase and phase to ground to see if the electricity will jump thru air or over an insulated material, which is where the words strike and creep come from which have their own formulas of what is acceptable and what isn't for manufacturing and installation. There's a little more room for creep obviously.
All that is to say, there's plenty of fancy new digital hi-pot testers. We rented one for a project that was going on a marine grade system. They'll run a test at whatever your parameters you type in and save it all to a flash drive. We worked for 8 hours to set up all of our testing jumpers and ran a test for 1 second on the control wiring for it to say PASS then we put it all back together.
The fancy one saves the leakage current values to the drive. Our analog one will only display it on an analog dial and we write it down. This is ok for testing AC (and this is where things start to get a little over my head), something about the RMS nature of AC causes more leakage current during the test, so generally we have a leakage value of let's say 1 milliamp. DC will generally only make microamps of current when we run the test. Try recording any kind of value when you look at the dial and it looks like it doesn't even move past zero haha.
We basically told the customer that we have a pass/fail tester and can't accurately produce any type of value for leakage on DC unless we rented or purchased another machine. But for 9 out of 10 times, it's fine that's all anyone cares about anyway. I've fucked up and left a plate somewhere it shouldn't have been and believe me you'll know when this thing fails lol. It sent 11kV thru a tiny circuit board, whoops