Implement groups api testing

[andrewtavis]

Terms

• I have searched open and closed feature requests
• I agree to follow activist's Code of Conduct

Description

Something that's needed to make sure that the test coverage is maintained for the backend is tests for the groups models. These could generally follow the example tests sent along in #824 and would be written in backend/entities/tests.py.

Contribution

Happy to answer questions or help implement as I can! 😊

[andrewtavis]

CC @thiagogquinto, @to-sta and I were thinking this would be a good next issue to look into as he needed to take over #801 :) Let us know if this'd be something that'd interest you!