These are some handy projects that can be used for printer testing.
Benchy
The classic boat benchmark.
https://www.thingiverse.com/thing:763622
All-In-One Printer Test
Full-size: https://www.thingiverse.com/thing:2656594
Mini: https://www.thingiverse.com/thing:2806295
Micro: https://www.thingiverse.com/thing:2975429