Ironically enough, first I wrote my code in Python, but then I decided to switch to Julia. When I made the switch, I tested the data structures generated in Julia against the data structures generated in Python. Now, I consider making my Julia package more user-friendly by adding normal testing and documentation. And, as it figures, this is a bad idea to have your tests depend on the completely different language.
I did not think about having some data pre-generated for tests. I am grateful to @heliosdrm for pointing this out.