DateHelper { static YearMonth calendarDayToYearMonth(CalendarDay calendarDay) { return YearMonth.from(calendarDayToLocalDate(calendarDay)); } private  DateHelper();   }
@Test public void calendarDayToYearMonth() { CalendarDay calendarDay = CalendarDay.from(2016, 10, 15); YearMonth expectedYearMonth = YearMonth.of(2016, 11); YearMonth actuaYearMonth = DateHelper.calendarDayToYearMonth(calendarDay); assertEquals(expectedYearMonth, actuaYearMonth); }