I have never been present to watch them do it. The state officers job is to test the pump, but the fuel still belongs to the station. I would expect them to either pay for it or put it back into the gas stations storage tank. Knowing how the state likes to pay for things, I can't imagine them doing that. So it seems like they should pour it back into the storage tank.

The state code actually spells out the testing procedure. They use a calibrated fuel can with a narrow neck and a glass vial on the neck, so they can see exactly how much fuel is in the can. And they use a calibrated thermometer to do temperature compensation. But it doesn't actually say what to do with the fuel after the test is finished.