Unit testing for Project Team Members router

[jng34]

Fixes #1892

What changes did you make and why did you make them ?

• wrote unit tests for projectTeamMembers.router
• edited the logic in the GET API route /project/:id/:userId in projectTeamMembers.router.js that incorrectly threw the HTTP code 400 when it should have been 200, which affected the unit test for that route

Screenshots of Passed Tests