Add unit tests for Issue and Comment Endpoints

[vaishnavi-gupta18]

Description

Add unit tests for Issue and comment API endpoints.

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

How Has This Been Tested?

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules

[amlannandy]

Nice work. LGTM.
One more thing we can do is add descriptions for each test. Maybe using doc strings?
Let's just merge this for now. We can pick that up later with other documentation stuff.