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.
The brakes are linked together and both the front hand brake and the rear brake pedal activates the left caliper. Here is my fist attempt at posting a picture that should make it obvious. Seems like either brake would activate the anti-dive unit.
Either will operate it, the front only operates it from the rotation of the front wheel and the lifting of the secondary master cylinder. Another way to test it would be to chock the front wheel so it can't roll and bounce the front end without appyling either brake and then apply the rear brake and see if it gets harder to bounce. Mine will almost lock up within the second bounce with the brake applied and bounces free without.