There is a guide I posted in my Froschkönig thread and one dude created a testing jig before (Belt tension test rig).
The belt tension of the guide on the other link (Measuring belt tension, squaring and calibration - Shapeoko - Carbide 3D Community Site) does not fit the MPCNC, they need much tighter belts, but the method in general is valid. The Prusa page makes it even more simple.