enhance: add unit test for string pk

[sunby]

#39107

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[mergify]

@sunby cpp-unit-test check failed, comment rerun cpp-unit-test can trigger the job again.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 81.02%. Comparing base (d2834a1) to head (8ed1c1b).
Report is 37 commits behind head on master.

Additional details and impacted files

@@             Coverage Diff             @@
##           master   #39329       +/-   ##
===========================================
+ Coverage   69.65%   81.02%   +11.37%     
===========================================
  Files         299     1408     +1109     
  Lines       26799   198565   +171766     
===========================================
+ Hits        18667   160894   +142227     
- Misses       8132    32014    +23882     
- Partials        0     5657     +5657     

Components	Coverage Δ
Client	79.50% <ø> (∅)
Core	69.56% <ø> (-0.09%)	⬇️
Go	82.95% <ø> (∅)

see 1131 files with indirect coverage changes