Add code coverage

[kamil1b]

Fix #32

[codecov-io]

Codecov Report

❗ No coverage uploaded for pull request base (master@e2bd827). Click here to learn what that means.
The diff coverage is n/a.

@@          Coverage Diff           @@
##             master   #34   +/-   ##
======================================
  Coverage          ?   69%           
======================================
  Files             ?     1           
  Lines             ?   100           
  Branches          ?     0           
======================================
  Hits              ?    69           
  Misses            ?    31           
  Partials          ?     0

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