@Test
 public void testAddToTail() {
   IntegerList list = new IntegerList(5);
   list.addToTail(6);
   assertEquals(6, list.getTailValue());
   assertEquals(5, list.getHeadValue());
 }
  @Test
  public void testGetTailValue() {
    IntegerList list = new IntegerList(5);
    list.addToTail(6);
    list.addToTail(7);

    assertEquals(7, list.getTailValue());
  }