That is correct Mike. To test an emergency generator you have to not only run the diesel but load it with part of the electrical distribution system and see how it goes. It is sometimes called a 'confidence run'. If anyone owns an emergency generator at home, they are being foolish if they don't run it every so often and put an electrical load on it - especially if it is hardwired to your house.
I imagine cruise ships usually load the emergency diesels with non-vital distribution boards/busses , such as power for crew areas or secondary systems. But I just learned Carnival Dream also puts primary loads on the emergency bus, which includes elevators and sewage systems and hence the brief problems with those.
I was on the Liberty Of The Seas a few months ago and they tested all the lifeboats on the starboard side one day while in a port. They were all in the water and running around, apparently practicing maneuvers they'd use in a real emergency to stay in a group.