Refactor test fixtures

Why these changes are being introduced:

The test suite was built piecemeal as the library grew,
and over time the fixture names were becoming clunky and
confusing.

How this addresses that need:

Rename, simplify, and reorganize test fixtures.  This
requires coordinated changes in tests, nearly entirely
just pointing at new fixture names.

Side effects of this change:
* None

Relevant ticket(s):
* https://mitlibraries.atlassian.net/browse/TIMX-526

Author: ghukill