Add unit tests

[LinuxSuRen]

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[codecov]

Codecov Report

Merging #284 (a4988e4) into master (0f23bd3) will increase coverage by 3.52%.
The diff coverage is 100.00%.

❗ Current head a4988e4 differs from pull request most recent head fdc2f25. Consider uploading reports for the commit fdc2f25 to get more accurate results

@@            Coverage Diff             @@
##           master     #284      +/-   ##
==========================================
+ Coverage   40.34%   43.87%   +3.52%     
==========================================
  Files          29       29              
  Lines        2015     2015              
==========================================
+ Hits          813      884      +71     
+ Misses       1167     1089      -78     
- Partials       35       42       +7     

Flag	Coverage Δ
unittests	43.87% <100.00%> (+3.52%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
pkg/common/util.go	84.31% <100.00%> (+50.98%)	⬆️
pkg/installer/check.go	33.92% <0.00%> (+7.39%)	⬆️
pkg/installer/process.go	15.84% <0.00%> (+15.84%)	⬆️

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