I generally test the elastic by puliing it out a fair way and releasing it in a controlled way. If the elastic goes back with reasonable tension all the way then that is good enough for me. I know a lot a match stars like to set their elastic quite tight to enable them to get the fish in quick but this also has the downside of potentially bumping fish off.
If you are not sure, why not get one of those bungs that allows you to alter the tension of the elastic to suit how you want it.
