The QB tanks come tested from the factory, so the only thing that needs to be tested is the stuff that I added to the tanks. In my case, that would be a return fuel line, the fuel level senders, and the tank covers. In one tank, where I started to install a flop tube, I cut an extra hole for the fuel level sender which I got to plug up.
Here is the right tank under pressure (about 2 PSI):
Here is the left tank under pressure. Notice that I never removed this tank from the wing. The rubber glove can be replaced with a standard balloon if you have one available.
I'm very happy to say that the tanks held pressure nicely. I hope to never see any nasty blue fuel stains on my tanks!