I tested one like this. I just used one of my cars that have power brakes and pluged the check valve into the test booster. Start car and test by pushing the brake rod in to simulate putting the brakes on. If it goes in easily, it's working. I also tested it by shutting off the car and waiting about 1 minute. Then pull check valve. If there is still vacuum, you've got a good one. 
Bob
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Bob
63 Impala 283/PG/3.36 (under restoration)
66 Impala 327/PG/3.36
66 Chevelle SS 409/M22/3.55
69 Chevelle 307/PG/3.08 (future restoration)
69 C10 short stepside 454/TH350/3.73
69 Custom 30 tow truck 350/4 spd/4.10 (resto done, CRUISIN TIME!)
71 Cheyenne 20 fleetside 350/4 spd/4.10
71 Chevelle 6/PG/3.08
72 Chevelle 454/M21/4.10
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