I never perform this test anymore the way it is described because of the potential damage that can result from a door not reversing. I use my forearm with my palm facing down to put under the door when it is several feet off the ground. Pay close attention to the bracket at the top of the door and the tension in the drive chain. If it is the screw type track, keep your eyes open for any resistance and listen for any noises indicating the hardware is not functioning properly. It doesn’t take but a fraction of a second for a garage door to start to self destruct doing this test. I have seen it happen in the past and it isn’t pretty. BTW…It wasn’t me or my client who did it…It was the seller!