here is one way.
You can run a basic function test of the antidive right from your dirver's seat. Put the bike in neutral and sit upon the seat with bike on level surface, your feet on ground. Hold the front brake lever firmly and physically pump the fornt forks with your body by thrusting. The front forks should normally collapse and then return to normal position. They should be free to move. Then, if you do this with gusto on several rapid sequences, then the front fork should lock as the brake caliper rotates and activtes the anti-dive plunger. If you are a big strong fella, that works pretty well, but smaller folks may not get enough rotation. That done; release the fornt brake lever and place your foot firmly on the brake peddle. Now your efforts to thrust the forks should be met with a solid lock of the forks. The rear brake should lock the forks, the front should not (unless you really go after it). If yours are locked, then you won't be able to collapse the forks.