The idea of this switch tester is to have one with the sides closed, as on a normal keyboard most sides of the case will be closed. As the switch tester I've found online have open sides and that this might change the sound the switch produces, I wanted to print one with the sides closed.
I also wanted to be able to expand my collection easily and still have them all together, so I added a simple slide-in mechanism to be able to expand the board as the collection goes on.

I've used PETG as this is what I most use for my prints but I suppose this could work with any other plastic filament. Same goes for the layer hight, I haven't tested other layer heights as this was printed with something that needed more granularity. As for infill, I would stick to the 15% or more, a less than the 15% most structures are empty and this might generate structure issues.

The key is a very basic print. It'll allow an emergency change or just to have a simple key to test the switches if needed.