Add test for serialize/deserializePrivateKey.

[dajiaji]

No description provided.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 89.90%. Comparing base (340359a) to head (c09010b).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #443      +/-   ##
==========================================
+ Coverage   89.33%   89.90%   +0.56%     
==========================================
  Files          58       58              
  Lines        4387     4387              
  Branches      413      415       +2     
==========================================
+ Hits         3919     3944      +25     
+ Misses        467      442      -25     
  Partials        1        1              

Flag	Coverage Δ
unittests	89.90% <ø> (+0.56%)	⬆️

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