[Testing] Add Model Tests for Resources and Tagging

[BethanyG]

Need to add specific model tests for Resources and Tagging, and provide framework going forward for those types of tests for other endpoints.

• CustomTag model - add tests for tag slugging #121
• Resource model

Adding these links, in case they're helpful:

• Testing Models with Django using PyTest and Factory-Boy
• Real Python: Django PyTest Fixtures
• Django Stars: Testing Your App with PyTest -- longer and more detailed article on PyTest in General and tips for Django testing with PyTest
• PyTest Docs
  pytest-django Docs

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.