Reduce duplication in the unit tests

[clumens]

This can be left until after other unit test PRs get merged. I'll have to update it, but I don't want to keep blocking those other PRs with my changes.

[clumens]

Hopefully we're just about at a point where we don't need to do anything to every test file. We're starting to have so many that it's obnoxious to do.

[nrwahl2]

Big fan

[clumens]

I've rebased this on master. It's good to go now.