I've got a couple of good used ones, I have them tested dynamically on a Machine at a store chain called Part Source here in Canada.
It simulates actually use being turned by the engine in that it spins the pulley and then the output is checked while spiningversus just strictly getting a reading using a multimeter or whatever.
I'd sell one for $40. plus shipping.
As I said I've got more than one so if someone else wants one, same deal on price.
PM me with a proper email if U want pics sent.