Add missing tests for edge cases

[kabirbaidhya]

Add missing tests for edge cases for better coverage.

[codecov-io]

Codecov Report

Merging #33 into master will increase coverage by 13.66%.
The diff coverage is n/a.

@@             Coverage Diff             @@
##           master      #33       +/-   ##
===========================================
+ Coverage   71.22%   84.89%   +13.66%     
===========================================
  Files           5        5               
  Lines         139      139               
  Branches       23       23               
===========================================
+ Hits           99      118       +19     
+ Misses         32       16       -16     
+ Partials        8        5        -3

Impacted Files	Coverage Δ
src/index.ts	70.9% <0%> (+7.27%)	⬆️
src/impl/domain.ts	93.5% <0%> (+19.48%)	⬆️

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[mesaugat]

Looks good. 👍