I had the feeling that my CoreXY printer was having precision issues that were tied to one motor. In CoreXY, each of the two motors for the X/Y movement control one diagonal, so having a model that runs precise diagonals allows for testing how each motor performs.

This model is designed to test a 0.4mm nozzle width, the structure is exactly 1 linethickness thick. 

Also, this model does not need any support and prints as is just fine.

Last but not least, the cutout triangle in the base tells you where the front left is, so that you can reconstruct which face faced which direction during printing even after removing the print.

As always, FreeCAD file is provided for you to tinker around with!