User endpoint tests

[carpecodeum]

Description

Added tests for User endpoints and fixed bug in UserManager.py to allow user to be deleted through the endpoint.

Related Issue #851

Motivation and Context

Tests should be present to allow the project maintainers to know that the endpoints arae working correctly.

How Has This Been Tested?

Screenshots (In case of UI changes):

Types of changes

• [ ] Bug fix (non-breaking change which fixes an issue)
• [x] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• [x] My code follows the code style of this project.
• [ ] My change requires a change to the documentation.
• [ ] I have updated the documentation accordingly.
• [x] I have added tests to cover my changes.
• [x] All new and existing tests passed.

[carpecodeum]

@JaDogg this is a draft PR. Should I refactor the rest of the tests in the same way? Your inputs are highly welcome.