Add test cases for generate_reports()

[JCantu248]

🗣 Description

This PR adds test cases for generate_reports() in tpt_reports.py. Resolves Issue #22

💭 Motivation and context

The added test cases will test ensure that negative boolean status values will be returned if load_json_file() returns a null JSON object, or if parse_json() was not able to parse out valid fields from the file and returns null objects.

🧪 Testing

Testing was performed by running PyTest and ensured all added and pre-existing test cases were passing.

✅ Pre-approval checklist

• This PR has an informative and human-readable title.
• Changes are limited to a single goal - eschew scope creep!
• All future TODOs are captured in issues, which are referenced
  in code comments.
• All relevant type-of-change labels have been added.
• I have read the CONTRIBUTING document.
• These code changes follow cisagov code standards.
• All relevant repo and/or project documentation has been updated
  to reflect the changes in this PR.
• All new and existing tests pass.

✅ Pre-merge checklist

✅ Post-merge checklist

[coveralls]

Pull Request Test Coverage Report for Build 6509751953

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 0.0%

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Totals
Change from base Build 6487626291:	0.0%
Covered Lines:	0
Relevant Lines:	0

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💛 - Coveralls

[dav3r]

I suggested a few small wording changes here.

[dav3r]

Looks good now! 👍

Note that if your pre-merge and post-merge checklists are empty, then those sections can be deleted. However, now that @nickviola is starting to version this repo, you should ensure that this PR updates the version appropriately.