TST/REF: Consolidate tests in apply.test_invalid_arg
- [x] Ensure all linting tests pass, see [here](https://pandas.pydata.org/pandas-docs/dev/development/contributing.html#code-standards) for how to run them

Moves relevant tests into test_invalid_arg. Had to rename two tests because they were of the same name, but no other changes. I organized the file by the reason for the exception, and indicated this at the top of the file. Certainly open to any other ways of organizing.
great. can you merge master to assure no actual failtures, ping on green. lgtm. can you merge master. thanks @rhshadrach 