Some practice in FreeCAD yielded a 4x4 switch tester.
Currently, the tester is a bit flimsy in the center, and the press-fit bottom has too tight of a tolerance. It'll still snap fit, but it'd highly depend on how steady of a print job you can manage to accomplish.
The design is also a bit sloppy and probably not idiomatic, as I don't know the best approach for design in FreeCAD.