test(path): improve test coverage

[mbhrznr]

working towards #3713.

this is a first pr to push the coverage of path/_common to 100%.
will work on follow-up prs to have the other parts of the module covered as well.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 92.16%. Comparing base (0ad578f) to head (57e9050).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5038      +/-   ##
==========================================
+ Coverage   92.10%   92.16%   +0.06%     
==========================================
  Files         487      487              
  Lines       38798    38796       -2     
  Branches     5432     5433       +1     
==========================================
+ Hits        35736    35758      +22     
+ Misses       3006     2983      -23     
+ Partials       56       55       -1     

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