What’s the “finger test” ???
It’s basically a test to see if your yoyo has any inherent wobble. If you throw a yoyo badly, you will cause it to wobble, but you can remove this wobble introduced by the throw by gently touching your finger in the gap or along the edge. The spin should smooth out. If it wobbles after that, you know it’s from the yoyo not being balanced perfectly.
It is a way to determine if your yoyo has a vibe or not