public static MonthsWindows months(int number) {
    return new MonthsWindows(number, 1, DEFAULT_START_DATE, DateTimeZone.UTC);
  }
@Test
  public void testDefaultWindowMappingFnGlobal() {
    MonthsWindows windowFn = CalendarWindows.months(2);
    WindowMappingFn<?> mapping = windowFn.getDefaultWindowMappingFn();

    thrown.expect(IllegalArgumentException.class);
    mapping.getSideInputWindow(GlobalWindow.INSTANCE);
  }