As long as they enjoy the testing and it's not terribly stressful for them or expensive for you, why not test? I don't think you *have* to test, but if you want to test, I don't think there's anything wrong with it.
I was in the talent search way back in the day, so I took a lot of tests. Personally, I enjoyed them. They were a fun challenge, and I really needed more challenge.
I'd say one test per semester is probably just about enough. But that's just my own opinion. I only let my kids be in one sport per semester, too. I figure it's comparable. <shrug>
