public void SpaceObjectObserverGetsUpdated() { var mockObserver = new Mock <ISpaceObjectObserver>(); var spaceObject = new SpaceObject(new Vector2(3, 2), new Vector2(1, 0)); spaceObject.AttachObserver(mockObserver.Object); spaceObject.Position = new Vector2(1, 7); spaceObject.Rotation = new Vector2(1, 4); mockObserver.Verify(observer => observer.ObjectUpdated(), Times.Exactly(2)); }