Add license-utilities tests + update attrToFull to act like attrToShort

[acagastya]

Fixes #125

Description

I have added various tests, I think 126 in total.

Other information

I have also updated license-utilities for an edge case:attrToFull({BY: undefined}) acts similar to attrToShort({BY: undefined})

Checklist

• My pull request has a descriptive title (not a vague title like Update index.md).
• My pull request targets the master branch of the repository.
• My commit messages follow best practices.
• I added tests for the changes I made (if applicable).
• I added or updated documentation (if applicable).
• I tried running the project locally and verified that there are no
  visible errors.

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[akmadian]

Wow! Ok that's a lot of tests! I'm happy that the tests are so stringent, it'll be good to have confidence that it's extremely unlikely that anything will get past them, but it's definitely almost too much. I think the amount of tests could easily be cut by 50 or 75%, and we would still be ok.

I'm gonna merge anyways since I think it's good to ere on the side of too many tests for this file since so much critical functionality is based on these utils.

Thanks for working on this :)

[acagastya]

You are welcome, @akmadian.