I have seen many test cubes on many sites, but no printable shearing test. I think this is important, especially on DIY printer kits.

After i assembled my Ender 3, made a bed leveling, the first print (dog) was flawles. Then a couple weeks later i realized that a printed solid box, or brick shape had a little shear. The two planes on the Y axis were rhombuses. It was not so bad, but i could see it. I printed a 20mm test cube, and measured 20mm on all opposing sides. But the diagonals of the cube were not equal. (It's good, for measuring size accuracy, but won't tell you if the X, Y an Z axes are perpendicular, or not) This happend because the X axis was not in parallel with the machine frame, i needed to loosen the bolts, and reassemble the whole X axis. I had only about 2-3mm difference on the sides.

So i made this simpe object, to simplify measuring diagonals. If the diagonals are not equal, the geometry of your machine is not good. The X, Y an Z axes are not perpendicular.

All this makes sense, if the printed object is part of a bigger project, or large parts must snap together. Deformity in the machine geometry could make big printed parts useless.

If you use your printer to print decorations, this kind of accuracy is not necessary.