Look into pytest env variables

[OliviaLynn]

We've been having trouble where environmental variables that are theoretically set in conf.py don't fully work in tests, which is remedied by explicitly setting them within the test. Not great that we have to do this.

Also, we may not want them to be so conditionally set in tests (with the ifs), this is worth taking a big picture look at as well.

[OliviaLynn]

Drew added a nice set_env_vars fixture, so I'll go through the unit tests to implement this throughout for consistency