If you are at a stop, put your tow vehicle in gear. Manually apply the trailer brakes. The tow vehicle should be at an idle speed, do not press the gas peddle. The trailer brakes should keep the vehicle from moving. If it does this, then your brakes are OK.
Slowly press the gas peddle and see how much resistance the trailer gives. There will be a point when the wheels will begin to turn. This depends upon the weigh of the trailer. The heavier the trailer, the sooner they will start rolling. But the engine of your tow vehicle will most likely need to be reved-up pretty good to move it from a stand still.
Try it, if you have resistance at idle from the trailer so the tow vehicle does not move, that's about as good as it gets.