  @Test
  public void addObjectAtOccupiedPosition() {

    boolean fail = false;
    model.addObjectAt(ru1, new Point(1, 1));
    try {
      model.addObjectAt(ru2, new Point(1, 1));
    } catch (final IllegalArgumentException e) {
      fail = true;
      assertThat(e.getMessage())
        .contains("Cannot add an object on an occupied position:");
    }
    assertThat(fail).isTrue();
  }