Make sure that all tests are unittest-compatible.

[mdickinson]

This PR is preparation for changing the continuous integration to use unittest instead of nose.

We had only a handful of nose-style tests (i.e., tests not based on TestCase); this PR changes those to use unit test, and makes some minor renames to avoid some not-tests being picked up by nosetests.

With these changes, I see exactly 569 tests on master, with both nosetests and unittest discover.

And yes, some of these tests are horrible and in need of more work. But not in this PR.

[rahulporuri]

LGTM except for one minor comment.

[codecov-io]

Codecov Report

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@@            Coverage Diff            @@
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  Branches          ?     1413           
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  Hits              ?     4616           
  Misses            ?     2021           
  Partials          ?      422

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