Add test on extra metadata

[mattiagiupponi]

References: #9859

corner case was missing

Checklist

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[etj]

To be squeezed and referred to issue #9842 in commit message

[codecov]

Codecov Report

Merging #9859 (1e2d0f6) into master (ca04bcf) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master    #9859   +/-   ##
=======================================
  Coverage   61.34%   61.35%           
=======================================
  Files         822      822           
  Lines       50300    50312   +12     
  Branches     7746     7746           
=======================================
+ Hits        30857    30869   +12     
  Misses      17764    17764           
  Partials     1679     1679