99 Protege brake issue

I just salvaged a 99 mazda protege 1.6l with 86k miles on it. The brakes function just fine, but there is almost no movement in the pedal. It's extremely hard. When I let off one of the bleeder screws to bleed them (4 wheel disc), the pedal has full range of motion again(can go to the floor) and bleeds just fine. No air in the lines, just some old fluid, but after bleeding all four wheels, the pedal still didn't want to go anywhere unless I put all my weight on it, and I'm not the smallest guy around either. I believe that sounds like a power booster failure, but I have never delt with one, so I was hoping for some other feedback and if there was a way to test the booster before I go replacing it.