The final test for the camera is to make sure it's electrically insulated. Of course, if it's waterproof it should also be electrically insulated; but there are degrees to which that might be true. Just as waterproofing is only good to a certain depth, insulation can be measured.

It's difficult to know a good measure of insulation but >100 Mega Ohms is suggested as as a lower limit. To test this I used a Supco M500 Insulation Tester (megohmmeter). With the camera submerged, I connected one lead to the positive power cable at the end of my cables, and put the other connectors in the water. My meter measured the resistance as > 1000 Mega Ohms; 10x the lowest acceptable level.

Success!

It's worth noting that if this test had failed in a significant way, the camera electronics would likely be fried. But then, if this test had failed, the electronics would eventually get wet and fry anyway.