Throw a ball, slam it into the rail and see if you can get 4 or more rebounds off the rail. That's up and down the table. For across the table you should be able to get 4 1/2 or more.
If you get those results the rails aren't dead.
r/DCP
This.
I'm not sure about the rail count, but if you do the above and get X rails, turn 180 degrees and use the mirrored rail, you should also get X off of it.
This works even if the table is made of chocolate.