The actual test for "wet location" stuff is to subject them to an artificial rain, with a pre-determined wind.
Typically, a trough will be set up about 7 ft. above the floor. This trough will have many, many 1/8" holes in the bottom, and a nail inserted into each hole. This causes the water to "drip" off.
A large fan is used to "suck" the rain at a particular angle- if memory serves me, this is about 15 degrees off vertical.
The item being tested is then subjected to this "rain" for a set period. "Passing" criteria vary somewhat by item, but the intent is to establish that there is no hazard created. Generally, some water entry is allowed.
