Honest answer? I would hope that the shelter would do that.
If you go as a total stranger to the dog and try to give it something and take it away or do things like put your hand in their food (sounds like the Sternberg assess-a-pet test, which even her OWN dogs couldn't pass) there is a good chance you could provoke a dog into resource guarding who has no issues at all. Shelter dogs are often stressed as it is.
Where I adopted my puppy they had a room kind of like a living room where you could sit and interact with the dog. Thing is, the dog was so excited over all the smells from the other dogs who had been in the room, it made it hard to get a good picture.
So I think I would ask to go for a walk while one of the shelter staff is holding the leash. You will get a chance to see how the dog is with someone familiar.
And I'd try to play with the dog, but I def wouldn't put my hand in its food dish.
Sorry if this wasn't too much help! This might be 'more than you wanted to know' but then again you might find it helpful:http://www.maddiesfund.org/organizat...ssessment.html