Test coverage for core.data_interface

[neilSchroeder]

Summary of changes and related issue

Testing and small fixes to core.data_interface

Relevant motivation and context

Fixing bugs, cleaning things up for good hygiene, test coverage to 90%.
Lots of single lines that aren't covered by other things. This will mostly be redone this summer. So this is good enough for now.

How to test

pip install pytest-cov
pytest tests/data_interface/ --cov=climakitae.core.data_interface --cov-report term-missing

be warned that this test takes a long time to run due to get_data

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update
• None of the above

To-Do

• Unit tests
  • Existing unit tests are passing
  • If relevant, new unit tests are written (required 80% unit test coverage)
• Documentation
  • Intent of all functions included
  • Complex code commented
  • Functions include NumPy style docstrings
• Naming conventions followed
  • Helper functions hidden with _ before the name
• Any notebooks known to utilize the affected functions are still working
• Black formatting has been utilized
• Tagged/notified 2 reviewers for this PR