Add unit tests

[zeckli]

As title.

[codecov]

Codecov Report

Merging #9 into master will increase coverage by 0.95%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master       #9      +/-   ##
==========================================
+ Coverage   59.52%   60.47%   +0.95%     
==========================================
  Files           4        4              
  Lines         210      210              
  Branches       42       42              
==========================================
+ Hits          125      127       +2     
+ Misses         84       82       -2     
  Partials        1        1

Impacted Files	Coverage Δ
src/utils/index.ts	100% <0%> (+33.33%)	⬆️

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