This is a test model for 3D printers.
Our object is to print 2 wheels, meet them together, and rotate them smoothly, like below.
https://youtu.be/KiCR8q_Z9a8

There are 3 points to be tested in this model.

How your print lines are clean (well retracted and well restarted).
A circle should be closed well, and should not be bridged to next circle.
If the circles are not clean enough, you can not meet them.

No back rush.
Back rush or vibration of timming belt leads distortion on the circles,
then you can not rotate them, if you cleared point 1.

Symmetry of X Y axes.
If your 3D Printer does not have enough symmetry or right angle in X Y axes,
it leads distortion on the circles, then you can not rotate them, if you cleared point 1. and 2.
It is not matter on cartesian printers, but sometimes problem on delta printers.