add more tests and comments

[SF-Zhou]

No description provided.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 100.00%. Comparing base (7196a54) to head (2838e6d).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff            @@
##              main        #8   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files            3         3           
  Lines          815       891   +76     
=========================================
+ Hits           815       891   +76     

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