@Override
 public void testGetContent() {
   assertEquals(sl, ul1.getContent());
   assertEquals(pn, ul2.getContent());
   assertEquals(rl1, ul3.getContent());
   assertEquals(rl2, ul4.getContent());
 }
 @Override
 public void testToString() {
   assertEquals(
       "an urgent letter whose content is a simple letter whose content is a text content (bla bla)",
       ul1.toString());
   assertEquals(
       "an urgent letter whose content is a promissory note letter whose content is a money content (100)",
       ul2.toString());
   assertEquals(
       "an urgent letter whose content is a registered letter whose content is a simple letter whose content is a text content (bla bla)",
       ul3.toString());
   assertEquals(
       "an urgent letter whose content is a registered letter whose content is a promissory note letter whose content is a money content (100)",
       ul4.toString());
 }
 @Override
 public void testGetCost() {
   assertEquals(SimpleLetter.SIMPLE_LETTER_COST * UrgentLetter.COSTFACTOR, ul1.getCost());
   assertEquals(
       (SimpleLetter.SIMPLE_LETTER_COST + pn.getContent().getAmount() / 100)
           * UrgentLetter.COSTFACTOR,
       ul2.getCost());
   assertEquals(
       (SimpleLetter.SIMPLE_LETTER_COST + RegisteredLetter.OVERCOST) * UrgentLetter.COSTFACTOR,
       ul3.getCost());
   assertEquals(
       (SimpleLetter.SIMPLE_LETTER_COST
               + pn.getContent().getAmount() / 100
               + RegisteredLetter.OVERCOST)
           * UrgentLetter.COSTFACTOR,
       ul4.getCost());
 }
  @Override
  public void testDoAction() {

    /* Before doAction */
    assertTrue(city.isEmpty());

    ul1.doAction();
    /* After doAction 1 */
    assertTrue(city.isEmpty());

    // ul2.doAction();
    /* After doAction 2 */
    // assertFalse(city.isEmpty());

    // ul3.doAction();
    /* After doAction 3 */
    // assertFalse(city.isEmpty());

    // ul4.doAction();
    /* After doAction 4 */
    // assertFalse(city.isEmpty());

  }