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.
• [x] My code follows the coding style guide.
• [x] I tested that my change works before raising the PR.
• [x] I have ensured that I did not break any existing API calls.
• [x] 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 :sweat_smile:

[github-actions[bot]]

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.

[Jaskowicz1]

Starting this PR during uni was an awful idea, might be a good idea to close this PR and restart it (annoying but there's conflicts now)

[Jaskowicz1]

Closing as this PR needs to be redone completely.