TST: Add regression tests for fixed issues
- [x] closes #14600
- [x] closes #14849
- [x] closes #14955
- [x] closes #14592
- [x] closes #12163
- [x] closes #12948
- [x] closes #15058
- [x] tests added / passed
- [x] passes `black pandas`
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`

lgtm. merge on green.