PizzaStore delivers pizzas. There are different implementations of pizza which are instantiated by the store before logic is executed on them (prepare, bake, cut,box)
PizzaStore depends on all pizza implementations. Changing the menu is trouble, because the store has to be modified all the time (violates open-closed priniciple ;))
(Unit-)Testing is hard, because we cannot inject mock-pizzas easily. (If you think this is still ok imagine a more detailed scenario where you have ingredients, an oven, a storage, suppliers for the boxes etc...you wouldn't want to test all this together, would you?)
