public void test_difference_hours() {
    Date d1 = Dates.newDate(2010, 1, 1, 12, 30, 0);
    Date d2 = Dates.newDate(2010, 1, 1, 10, 0, 0);
    assertEquals(2, Dates.differenceHours(d1, d2));

    Date d3 = Dates.newDate(2010, 1, 1, 12, 30, 0);
    assertEquals(0, Dates.differenceHours(d1, d3));
  }