Air Brake inspection question.?

Ok I'm taking my class b test soon, but I'm still wondering which gear to put the truck in after I finish checking the governor cut out. I know I need to turn the engine off and turn the key to the on position, push in the parking brake, but I'm still not sure what gear it needs to be in. I'm thinking that it's neutral, but I'm not sure. Keep in mind the truck I'm testing on is an automatic. I appreciate any help, thanks.