I use Rick's method to test, its the easiest way to see if any fogging is apparent. Though I prefer to do it without any safelights on, just to remove another potential variable. If there is fog, and depending on how much, you can try restrainers to keep the whites. I use Potassium Bromide (KBr) as its pretty cheap. mix with water to create a 10% solution and add to a developer of your choice. Increase the concentration until you can get whites. Sometimes if the paper is to far gone this will not work even if you add a ton of KBr.