Add Unit Testing

[BetaHuhn]

With #219 recently causing the action to fail in production I believe it is time to add proper automated tests to this project.

Previously I only tested the action manually on each contribution or feature addition, but the action wasn't tested for automated dependency updates coming from Dependabot. In the future I would like all code changes to be tested before landing on master and being released to production.

Since the action uses both the GitHub API as well as the GIT protocol under the hood to synchronize your repositories, I am not sure how to best test the action. With this discussion I am looking to gather some feedback and recommendations on how to do this.

If anyone has experience with testing GitHub Actions and wants to contribute to this project, feel free to work on this yourself!
I'd be happy to review a PR and help with writing tests.

Thanks!