Add tests for the versioning model

[webbertakken]

Need to bump the quality a little bit again after #80

[codecov]

Codecov Report

Merging #81 into master will increase coverage by 29.37%.
The diff coverage is 100.00%.

@@             Coverage Diff             @@
##           master      #81       +/-   ##
===========================================
+ Coverage   54.78%   84.15%   +29.37%     
===========================================
  Files          13       14        +1     
  Lines         188      202       +14     
  Branches       33       39        +6     
===========================================
+ Hits          103      170       +67     
+ Misses         77       29       -48     
+ Partials        8        3        -5     

Impacted Files	Coverage Δ
src/model/versioning.js	80.30% <100.00%> (+80.30%)	⬆️
src/model/input.js	100.00% <0.00%> (ø)

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