public Calendar ceil(long t) {
        Calendar cal = new GregorianCalendar(Locale.US);
        cal.setTimeInMillis(t);
        return ceil(cal);
    }
@Test
    public void testCeil1() throws Exception {
        CronTab x = new CronTab("0,30 * * * *");
        Calendar c = new GregorianCalendar(2000, Calendar.MARCH, 1, 1, 10);
        compare(new GregorianCalendar(2000, Calendar.MARCH, 1, 1, 30), x.ceil(c));

        // roll up test
        c =     new GregorianCalendar(2000, Calendar.MARCH, 1, 1, 40);
        compare(new GregorianCalendar(2000, Calendar.MARCH, 1, 2, 0), x.ceil(c));
    }