Adding tests to Util

[jukent]

PR Summary

First pass at tests for util.py Closes #126

PR Checklist

General

• [x] Make an issue if one doesn't already exist
• [x] Link the issue this PR resolves by adding closes #XXX to the PR description where XXX is the number of the issue.
• [x] Add a brief summary of changes to docs/release-notes.rst in a relevant section for the next unreleased release. Possible sections include: Documentation, New Features, Bug Fixes, Internal Changes, Breaking Changes/Deprecated
• [x] Add appropriate labels to this PR
• [x] Make your changes in a forked repository rather than directly in this repo
• [x] Open this PR as a draft if it is not ready for review
• [x] Convert this PR from a draft to a full PR before requesting reviewers
• [x] Passes precommit. To set up on your local, run pre-commit install from the top level of the repository. To manually run pre-commits, use pre-commit run --all-files and re-add any changed files before committing again and pushing.

[jukent]

Currently there are some place holder functions in here and I did not generate the requisite images yet, just creating this PR so that my work so far is visible.

[jukent]

I would love to replace some of the datafiles accessed will simpler dummy data, but because of the lat/lon grids and skewt plots, it seemed easier to access these small datafiles.