..I'm finishing up a total brake overhaul (rebuilt all calipers with O Rings and all new lines and hoses except front to rear hard line which requires removal of body)   I noticed the master cylinder leaking where it connects to the power booster so I bought a new master.  The booster looks OK - I took it out for cleaning and repainting, but wondering if there is a way to test it with a vacuum pump or some other way before I put it back in only to find it is bad (you know what a pain removing and installing it is!)  The car is not running at this point so I can't test it by starting the engine and comparing pedal feel while running vs. not running as I've read elswhere.  Suhggestions?

I used a air operated vacuum pump I bought at Harbor Frieght. Hooked it up to my air compressor, adjusted air pressure so I had about 15 # vacuum and tested all my vacuum lines on my 72 -- without the engine running . Hope it helps. Big Al

Yeah..really about all you can do is see if it will hold vacuum. You can't really test to see if it actually works, per-se. It should hold a good vacuum for quite a while, but don't know off-hand if there is a specific spec for how long.....
There is probably some info on that in the Service Manual, tho. I can look this evenin when I get home.