CLN: cleanup, deduplicate plotting/test_frame
- [ ] closes #xxxx
- [ ] tests added / passed
- [ ] passes `black pandas`
- [ ] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [ ] whatsnew entry

1. Make more reasonable var names
2. Get rid of one test in favor of parametrization in another one
thanks @ivanovmg very nice