Refactor tests

[Naapperas]

Closes #169

This attempts to fix and "normalize" the many tests we have on NIJobs in order to make them more manageable.

[render]

Your Render PR Server URL is https://nijobs-backend-pr-311.onrender.com.

Follow its progress at https://dashboard.render.com/web/srv-cfvt1se4dad04sqe6730.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (f698ee0) 90.33% compared to head (f23a0e1) 90.45%.
Report is 1 commits behind head on develop.

❗ Current head f23a0e1 differs from pull request most recent head 5bd79a6. Consider uploading reports for the commit 5bd79a6 to get more accurate results

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #311      +/-   ##
===========================================
+ Coverage    90.33%   90.45%   +0.12%     
===========================================
  Files           54       54              
  Lines         1469     1477       +8     
  Branches       245      245              
===========================================
+ Hits          1327     1336       +9     
+ Misses         137      136       -1     
  Partials         5        5              

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[Naapperas]

After refactoring work on this PR is finished, I am going to write documentation regarding how contributors should write tests.

[Naapperas]

Looks like we will still need to wait for a new version of fast-xml-parser