fix: cleanup and refactor tests

[sainak]

Proposed Changes

• remove testmixin
• create objects only when required
• use dummy cache backend for tests

Merge Checklist

• Tests added/fixed
• Update docs in /docs
• Linting Complete
• Any other necessary step

Only PR's with test cases included and passing lint and test pipelines will be reviewed

@coronasafe/care-backend-maintainers @coronasafe/care-backend-admins

[codecov]

Codecov Report

Patch coverage has no change and project coverage change: +10.12% 🎉

Comparison is base (40484cf) 48.49% compared to head (685a98a) 58.61%.

❗ Current head 685a98a differs from pull request most recent head 2cfecf1. Consider uploading reports for the commit 2cfecf1 to get more accurate results

Additional details and impacted files

@@             Coverage Diff             @@
##           master    #1584       +/-   ##
===========================================
+ Coverage   48.49%   58.61%   +10.12%     
===========================================
  Files         683      205      -478     
  Lines       14359    11068     -3291     
  Branches     2518     1566      -952     
===========================================
- Hits         6964     6488      -476     
+ Misses       7182     4375     -2807     
+ Partials      213      205        -8     

see 489 files with indirect coverage changes

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