[Mobile] Added tests for all used API Endpoints

[amlannandy]

Description

This PR adds Unit Tests for all the endpoints being used by the Mobile Application. Each commit covers tests for a separate section of the API (profile. project, team etc).
Also build_runner package had to be added as a dev dependancy as after null safety, the Mock API class has to be created using it.

Fixes #595

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?

Test Configuration:

• VSCode Testing Extension
• Windows 10

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