Need to add unit tests for utility schemes

Given the implementation of a unit testing framework for the atmospheric_physics repo in PR #78, there is now an opportunity to create some unit tests for the various physics schemes inside the `utilities` directory.

This would be particularly beneficial because the tests done in CAM-SIMA are usually for an entire physics suite, where the utility schemes are grouped together, as opposed to each individual utility scheme as proposed here. Plus it would allow for additional test coverage for a PR without necessarily requiring the user to run CAM-SIMA.