⚙️ Add tests for BackupManager

[swiftyfinch]

Description

I've added tests for BackupManager.

References

• #236

Checklist (I have ...)

• 🧐 Followed the code style of the rest of the project
• 📖 Updated the documentation, if necessary
• 👨🏻‍🔧 Added at least one test which validates that my change is working, if appropriate
• 👮🏻‍♂️ Run make lint and fixed all warnings
• ✅ Run make test and fixed all tests

❤️ Thanks for contributing to the 🏈 Rugby!

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (af77cad) 42.84% compared to head (2841fb9) 45.00%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #300      +/-   ##
==========================================
+ Coverage   42.84%   45.00%   +2.16%     
==========================================
  Files         142      142              
  Lines        4166     4166              
==========================================
+ Hits         1785     1875      +90     
+ Misses       2381     2291      -90     

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