Add unit tests for ModelViews

[pleonex]

Is your feature request related to a problem? Please describe.
Since the work on this program started as experimental, there aren't unit tests.
The work should happen once all the development for the initial release is done, so we are sure this is the design of the tool we want.

Describe the solution you'd like
Implement unit tests for every view model and model class. Use the NUnit3 framework as the rest of repositories. Take into account the code coverage.

Describe alternatives you've considered
UI testing is complex and expensive to maintain. It could be considered but at very much later stage.