@Test
public void testSub() throws Exception {

    ISODate isoDate1 = new ISODate("2013-10-10T13:20:40Z");
    ISODate isoDate2 = new ISODate("2013-10-10T13:21:40Z");
    assertEquals(60, isoDate2.timeDifferenceInSeconds(isoDate1));
    isoDate2 = new ISODate("2013-10-10T13:19:40Z");
    org.junit.Assert.assertEquals(-60, isoDate2.timeDifferenceInSeconds(isoDate1));
}