Every lifter should be able to hang from a pull-up bar for 30 seconds. If you can't then you need to work on grip strength... and maybe lose some of that useless dead weight. (That would be fat). Aside from grip strength, the hanging test might highlight some shoulder and spinal issues.
Can you do that easily? Good. Now try this: Hang from the bar for thirty seconds. When the timer rings, do a pull-up. If you can do that, you're not too bad.
Now let's ramp it up. Without letting go, drop back down and hang for another thirty seconds and do a second pull-up. For the true crazies, let's see who can do 10 of these 30-second hang pull-ups. Few can "hang" for over five minutes. Can you?