The true test is not whether they both spin in the same direction - you have to try and HOLD one tight while turning the other. IF you can't keep it both moving, it's a posi.
I have an 8" rear end from a '78 six cylinder that I thought was a posi, because both axles turned in the same direction. It is not. A true posi will turn both axles regardless of whether you try and keep them from moving. A non-posi can turn both in the same direction, especially when off the ground, but it is misleading.
Chris