I have the same concern as Gael: vars1/vars2 is really obscure. I would even prefer X and y, if one thinks in terms of skl conventions. Sorry If somebody asked you to mv from "tested_vars" / "target_vars" to "vars1" and "vars2", but this was a mistake for sure. 
Using (tested_vars/target_vars) does not limit the applicability of f statsitics, and,
Most importantly, (vars1/ vars2) is not consistent with the conventions of the module.