Keep doing the prescribed alcohol test - if it passes use the fuel.
The only "prescribed" alcohol test I know of for GA is where you put a measured amount of water and a measured amount of fuel into a container. Stir or shake vigorously, let it settle and see if the "apparent" fuel/water ratio has changed.
Sounds good in theory, but with a potential alcohol content of 2.5%, or possibly up to 10% in some places, it doesn't come across as a huge potential change in the ratio. Plus you need a see-through container that can be sealed properly and is resistant against everything that may be added to the fuel, and a very accurate way to either measure the fuel beforehand, or write on the container to see what the start and end levels are.
Does anybody have practical experience using this method? Particularly of course if you actually found alcohol so you've proven the method to work. Any tips? What sort of container do you use?