test: add unit test

[yakumioto]

No description provided.

[codecov]

Codecov Report

Attention: Patch coverage is 92.30769% with 3 lines in your changes are missing coverage. Please review.

Project coverage is 73.86%. Comparing base (52012f3) to head (3b02936).

Files	Patch %	Lines
hmac/hmac_sha.go	90.32%	0 Missing and 3 partials ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##             main       #5       +/-   ##
===========================================
+ Coverage   63.76%   73.86%   +10.09%     
===========================================
  Files           9        9               
  Lines         839      838        -1     
===========================================
+ Hits          535      619       +84     
+ Misses        214      129       -85     
  Partials       90       90               

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