I don't know of any lab testing that can be done at home, outside of simple mechanical testing done in an engine.
My guess is that the fuel is now being winterized, which may have an adverse affect on it's effective levels.
They use all kinds of stuff to bump the effective level of burning and detonation resistance. Gasoline is formed out of Heptane, Octane and Ethanol, as well as other components. Lead was a big one, but the fallout over cities kept it from continuing.
I highly doubt that in Phoenix, AZ you are getting much water in the tank, but you can always shake it in a clear bottle and let it sit, to look for separation. I've done that and I have a blacklist of gas stations that I will not go to, because of ground water content.
