This is an example .NET solution that defines an object oriented model in a .NET Standard class library. The model is accompanied with unit tests created with xUnit.
The unit tests can be given to students in order to learn to implement the model based on the specification.
There is also a visualisation in WPF, which demonstrates how the model can be used in a graphical user interface by means of the MVVM design pattern. The model can be used in multiple ways: you can try to solve the puzzle by hand or a solution can be stepped through or replayed.
There are two unit test classes. One is based on reflection and contains descriptions of what needs to be constructed. The other makes the build fail if the model is not implemented.