Improve Backend Test Coverage to 95%+

[HarshitVerma109]

Increase backend test coverage from 91% to 95%+ by adding tests for uncovered models, mixins, managers, and API nodes.

[HarshitVerma109]

Hi @arkid15r,
Could you please assign this issue to me ?

[arkid15r]

Could you also make sure our external (REST) API coverage is 100%

apps/api/rest/v0/chapter.py                                                       44      4      2      0  86.96%   95, 115-122
apps/api/rest/v0/committee.py                                                     35      4      2      0  83.78%   66, 86-96
apps/api/rest/v0/common.py                                                        12      0      0      0 100.00%
apps/api/rest/v0/event.py                                                         42      6      4      0  78.26%   89-94, 114-117
apps/api/rest/v0/issue.py                                                         50      0      8      0 100.00%
apps/api/rest/v0/label.py                                                         23      4      2      0  76.00%   61-66
apps/api/rest/v0/member.py                                                        44      4      2      0  86.96%   81, 101-104
apps/api/rest/v0/milestone.py                                                     54      0      8      0 100.00%
apps/api/rest/v0/organization.py                                                  35      4      2      0  83.78%   73, 97-103
apps/api/rest/v0/pagination.py                                                    27      0      2      0 100.00%
apps/api/rest/v0/project.py                                                       49      7      4      0  79.25%   103-112, 132-139
apps/api/rest/v0/release.py                                                       48      0      8      0 100.00%
apps/api/rest/v0/repository.py                                                    42      8      2      0  77.27%   76-81, 102-108
apps/api/rest/v0/snapshot.py                                                      97      1     12      0  99.08%   124
apps/api/rest/v0/sponsor.py                                                       39      4      2      0  85.37%   84, 104-107
apps/api/rest/v0/structured_search.py                                             40      7     10      3  80.00%   55, 64-66, 75, 91-94