This is a simple model to test your bed level and adhesion. It's roughly 200x200 and fits the Ender 3 and Ender 3 Pro bed perfectly. It's ofcourse usable on any printer with a print bed of size 220x220 or larger. I use it to track down bed leveling issues like warping and poor adhesion.

If you print it on an Ender 3/Pro with "Quality -> Layer height" set to 0.2 and slice it with Cura you will get a model with exactly one slice. This makes any bed levelling issues very visible. It only takes 10-12 minutes to print it.

I've included the Fusion 360 file and also a STEP version of it if you wish to adapt it to your own needs.

Enjoy!