Some unit tests have recently regressed, in part due to output changes

in recent versions of some of the tools we call.
cpplint and flake8 had some string changes, which are harmless, but

broke the test suite. We now test against the updated strings.
Something with the temp directory management also changed. I'm not sure

why it wasn't broken before, but basically, modules were importing

tmpdirs and tmpfiles for testing, and these global variables

themselves were being overridden when cleaning up the temp dirs/files.

This meant that modules were hanging onto old copies. Now, we keep the

same instances around, and they're just cleared.

Unit tests pass on Python 2.7 and 3.6-3.10.