Without specialized equipment it’s impossible to test the diaphragm or the associated internal valves of the booster. The only thing you can check on the booster with the master cylinder removed is that the movement of the power rod that goes through its center and connects to the master cylinder is operating unrestricted. You might want to test for that since your pedal was sticking to the floor, however I’d bet the sticking is caused by the master cylinder.
The way the master cylinder is made, it consists of two pistons in a chamber, the forward surface of the pistons being what transfers the pressure to the calipers, the back surface of the pistons being what draws fresh fluid from the vented reservoir and keeps the MC full. If the piston seals, which are rubber, are deteriorated, they can become stuck in the cylinder and prevent the piston from withdrawing.
Now c’mon, junior, you’ve visited before. You know we can better help with if we know the year, make, model and mileage. Are the answers are…? We’re always happy to help, but we can better do so if we know something about the vehicle.