DO NOT rely on a tug test. GET OUT AND LOOK at the fifth wheel jaws from behind - that is what keeps your trailer from coming unhooked - so do not trust anything else. Use a flashlight if necessary. If you don’t see the jaws locked behind the kingpin, it isn’t hooked and you should NOT move the trailer until it is. Separation of units happens far more often than you could imagine, and it’s absolutely preventable.