RichModel2

RichModel2.java

public class OrderTest {

  /**
    * This test shows that a rich model gurantees that it is in a legal state
    * at any time.
    */
  @Test
  public void richDomainModelMustEnsureToBeConsistentAtAnyTime() {
    Order order = new Order();
    BigDecimal total = order.getTotal();

   /*
     * A new order has no items and therefore the total must be zero.
     */
    assertEquals(BigDecimal.ZERO, total);

    OrderItem aGoodBook = new OrderItem(new BigDecimal("30"), 5,
     "Domain-Driven");
    List<OrderItem> items = order.getItems();

   try {
     items.add(aGoodBook);
   } catch (UnsupportedOperationException e) {
    /*
      * We CAN NOT BREAK ENCAPSULATION, because the order object will not
      * expose it's internal state to clients. It takes care about it's
      * state and ensures that it is in a legal state at any time.
      */
   }

   /*
     * We have to use the object's mutator method
     */
    order.addItem(aGoodBook);

   /*
     * After we added an OrderItem. The object is still in a legal state.
     */
    BigDecimal totalAfterItemAdd = order.getTotal();
    BigDecimal expectedTotal = new BigDecimal("150");

    assertEquals(expectedTotal, totalAfterItemAdd);
  }
}