@Test
  public void testCompareTo() {
    StopWatch s1 = new StopWatch(5, 59, 300);
    StopWatch s2 = new StopWatch(6, 01, 200);
    StopWatch s3 = new StopWatch(5, 50, 200);
    StopWatch s4 = new StopWatch(5, 59, 300);

    assertFalse(s1.equals(s2));
    assertTrue(s1.equals(s4));

    assertTrue(s2.compareTo(s1) > 0);
    assertTrue(s3.compareTo(s1) < 0);
    assertTrue(s1.compareTo(s4) == 0);
  }
  @Test
  public void testMutate() {
    StopWatch s1 = new StopWatch(5, 59, 300);
    StopWatch s2 = new StopWatch(5, 59, 300);

    StopWatch.setMutate(false);

    s1.add(1000);
    s1.setMilliseconds(100);
    s1.setSeconds(50);
    s1.setMinutes(2);
    s1.add(s2);

    assertTrue(s1.equals(s2));
  }
  @Test
  public void testEqual2() {
    StopWatch s1 = new StopWatch(5, 59, 300);
    StopWatch s2 = new StopWatch(6, 01, 200);
    StopWatch s3 = new StopWatch(5, 50, 200);
    StopWatch s4 = new StopWatch(5, 59, 300);

    assertFalse(StopWatch.equals(s1, s2));
    assertFalse(StopWatch.equals(s1, s3));
    assertTrue(StopWatch.equals(s1, s4));
    assertFalse(StopWatch.equals(s2, s3));
    assertFalse(StopWatch.equals(s2, s4));
    assertFalse(StopWatch.equals(s3, s4));
  }