REF: separate bloated test
Working on logical ops I'm finding a bunch of internal inconsistencies that will need to be addressed.  Since those are liable to have large diffs, this starts off with refactor that leaves behavior unchanged: simplify the method itself, and split a giant test into well-scoped ones.

> Perhaps we could clear out some of the TODO's you added in this PR in the PR itself though.

Separate PR(s).  Lots of small steps. thanks @jbrockmendel 