My own preference is to keep tests inside the same file for my course projects. (When you start writing large programs — like the ones I used to assign in our Fundamentals 1 — consider reading https://felleisen.org/matthias/Thoughts/Modular_Programming.html for this kind of programing.)
The Racket standard is to split packages into three parts: code, tests, docs so that people allergic to receiving more than absolutely necessary can just ge the code.