If you are just replacing an existing bath waste/overflow with a new one, a draining test will work. This test is completed by closing the stopper and filling the tub with cold water until it starts to flow through the overflow plate, and then shut off water and inspect all connection points behind the tub. Use cold water for energy savings. If the bath waste/overflow are part of a larger plumbing system installation, reach out to your local building officials to find out what type of test is required.
