add test for non vacant `MetadataStorage` `insert`

[tcoratger]

trafficstars

Checklist

• [ ] Linked to Github Issue
• [ ] Unit tests added
• [ ] Integration tests added.
• [ ] This change requires new documentation.
  • [ ] Documentation has been added/updated.

[codecov-commenter]

Codecov Report

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

Project coverage is 88.57%. Comparing base (9d34f50) to head (c749b24).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #624   +/-   ##
=======================================
  Coverage   88.56%   88.57%           
=======================================
  Files         120      120           
  Lines       35375    35393   +18     
=======================================
+ Hits        31330    31349   +19     
+ Misses       4045     4044    -1     

:umbrella: View full report in Codecov by Sentry.
:loudspeaker: Have feedback on the report? Share it here.

[tcoratger]

@igaray Is there anything missing here?