public static DaysWindows days(int number) {
    return new DaysWindows(number, DEFAULT_START_DATE, DateTimeZone.UTC);
  }
@Test
  public void testDaysCompatibility() throws IncompatibleWindowException {
    CalendarWindows.DaysWindows daysWindows = CalendarWindows.days(10);
    daysWindows.verifyCompatibility(CalendarWindows.days(10));
    thrown.expect(IncompatibleWindowException.class);
    daysWindows.verifyCompatibility(CalendarWindows.days(9));
  }