Add Unit tests

[mathisonryan]

Are you willing to contribute it (Yes/No): Yes

Describe the feature and the current behavior/state.
Add unit tests so that we can setup github actions to ensure commits don't break existing functionality.

Will this change the current API? How?
No
Who will benefit with this feature?
Everyone that uses in-toto-dbom-wrapper as it helps ensure the stability as updates are committed.
Miscellaneous Information