public TestModelService(IModelRelationshipFactory modelRelationshipFactory)
     : base(modelRelationshipFactory)
 {
     ItemGroups = ImmutableList <IImmutableList <IModelNode> > .Empty;
     StartNewGroup();
 }
 protected ModelServiceBase(ModelStore modelStore, IModelRelationshipFactory modelRelationshipFactory)
 {
     ModelStore = modelStore;
     ModelRelationshipFactory = modelRelationshipFactory;
 }