It is amazing that some people avoid flood testing their waterproofing installations prior to tiling. It is inexpensive insurance and can save you a great deal of expense and time. And, if you install NobleSeal or Chloraloy, you should have a watertight installation for the life of the tile. Major plumbing codes require tiled showers to be flood tested.
The procedure requires filling the pan with water to the top of the rough threshold and checking for leaks. Since most leaks occur at the drain, it is prudent to test the area around the drain prior to filling the rest of the pan with water. A test plug should be used to plug the drain below the weep holes. An image of a typical plug is below. Test plugs are available at plumbing supply houses, many hardware and big box stores.
Flood tests are generally 24 hours. Some plumbing inspectors will want to pull the plug themselves to check for proper sloping of the waterproofing membrane and verify that weep holes are clear. Check with plumbing inspectors for requirements in your area.