How do I troubleshoot my brake booster?

Hey all, I apologize if this has been covered before, I tried searching a bit and couldn’t find really any specific info on this.

The other day I was moving cars around the driveway, and noticed my '74 Barracuda had little to no brakes. The first few presses of the pedal were okay, but I quickly lost all braking power. Luckily, I was only idling in and out of the driveway, and shifting into park was an easy solution.

I checked the fluid, level was good. This led me to the brake booster. The vacuum line is in good condition and connected firmly to the booster and carb. I'm wanting to know the proper procedure to troubleshoot the booster, as I suspect the diaphragm may be leaking. Any tips?