NFPA 72 requires testing every device at the end of the project and many project specs / contract documents require it too. Most of the time the AHJ just tests a small percentage if you can show that you pre-tested 100%. Wouldn't you want to test before someone else might, to be sure it works anyway.
Absolutely test everything. Depending on complexity, you may have to test some items multiple times. In NYC, any waterflow has to put the elevators into recall. Got 20 risers? Elevators are going to the primary recall floor 20 times. You can lose your shirt if you don't think this part through.