refactor: cleaned up unit-tests

[Jaskowicz1]

This PR cleans up unittest.cpp, closing: #936

Code change checklist

• I have ensured that all methods and functions are fully documented using doxygen style comments.
• My code follows the coding style guide.
• I tested that my change works before raising the PR.
• I have ensured that I did not break any existing API calls.
• I have not built my pull request using AI, a static analysis tool or similar without any human oversight.

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[Jaskowicz1]

Accidentally put this branch on the main D++ repo, whoops 😅

[github-actions]

This pull request has had no activity and is being marked as stale. If you still wish to continue with this pull request please comment to reopen it.