Add tests to AddTeamMember APIView

[Oksamies]

Current dependencies on/for this PR:

• master
  • PR #928
  • PR #947
  • PR #930
    • PR #929 👈

This stack of pull requests is managed by Graphite.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (c87724d) 92.43% compared to head (3e3baba) 92.53%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## 12-05-Add_AddTeamMemberAPIView_to_api_URLs #929 +/- ## ============================================================================== + Coverage 92.43% 92.53% +0.09% ============================================================================== Files 275 275 Lines 8168 8168 Branches 773 773 ============================================================================== + Hits 7550 7558 +8 + Misses 513 505 -8 Partials 105 105 ```

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