WordCloudViewModel.GetNewColor() is now fully functional and IsNotNull tested. Brush property added to WordModel, which returns a new SolidColorBrush with the Color property as the argument. An IsNotNull test was added to this. For some reason I don't entirely understand, instantiating SolidColorBrush objects is done on or modifies the UI thread, which is a no-go on unit tests. this necessitated the addition of a global SynchronizationContext in the App section.