Why print a boring test cube when you can print a usable dice at the same time!
Prints a 15mm customizable cube that is ideal to test printer dimensional accuracy, cooling, ringing, flow rate, temperature etc. If the cube prints smoothly, measures 15mm on all axes, has well-defined number edges and no noticeable ghosting or ringing your printer and filament settings are well tuned.
Print the sample, or change the parameters in OpenSCAD and generate the required stl file for rounded or traditional square-edged dice and embed any character in the face of the dice.