CLN: Split pandas/tests/base/test_ops.py
As suggested by @jreback in [this PR comment](https://github.com/pandas-dev/pandas/pull/32725#issuecomment-599299873)

- [x] tests added / passed
- [x] passes `black pandas`
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
