Add tests

[tuyentv96]

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[codecov]

Codecov Report

Attention: Patch coverage is 80.00000% with 2 lines in your changes missing coverage. Please review.

Project coverage is 70.39%. Comparing base (fde8499) to head (301bf7d).
Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
src/cron.rs	77.77%	2 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           master      #12       +/-   ##
===========================================
+ Coverage    0.00%   70.39%   +70.39%     
===========================================
  Files           4        4               
  Lines         163      152       -11     
===========================================
+ Hits            0      107      +107     
+ Misses        163       45      -118     

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