That's the way I test them too... except that I grab them with a huge pair of slip joint pliers. The reason being is that some of them are just as broken, but they can't be turned by hand. If the magnet outer moves independently of the steel hub, even a tiny, tiny bit, then they must
be replaced. There is absolutely no repair.
I test them anytime the rotor is removed for a primary chain replacement or whatever. The incidence of failure is way to high to not have this as a regular check.