To test the reverse mechanism of your garage door, it is the safest to use a paper towel roll, because they are soft and they are not strong enough to hold up any door, not even a doggy door, and it is a good way to find any obstruction that does not offer a lot of resistance. Just put the roll in the threshold of the garage door, and push the button to close it. When it touches the roll, the mechanism should lift up again and the door should open. As such, the paper towel roll should not be damaged, or at least not a lot.
Of course, it is vital to check your garage door monthly. First you have to check the springs, because the springs carry heavy loads and they need to be strong, otherwise the heavy door can’t be lifted. You will have to look at whether the springs are rusted, are they broken, or are they fine? Then you look at the door itself, and whether or not there are rusted edges or sharp edges, which can possibly hurt someone. Lastly, you must look at the pulley system to ensure it is in good shape. Applying chain lubricant is always a good idea too.