@Test
  public void testDayClassFunction() {
    int tuesdayDay = 3;
    calendarAttributes.set(CalendarAttributes.dayClassFunction, "yellowTuesdays");
    // switch to next month to refresh classes
    calendar.openPopup().getHeaderControls().nextMonth();
    DayPicker proxiedDayPicker = calendar.openPopup().getProxiedDayPicker();
    CalendarDays tuesdays = proxiedDayPicker.getSpecificDays(tuesdayDay);
    tuesdays.removeSpecificDays(DayType.boundaryDay);

    for (CalendarDay tuesday : tuesdays) {
      assertTrue(tuesday.containsStyleClass("yellowDay"), "All tuesdays should be yellow.");
    }

    calendarAttributes.set(CalendarAttributes.dayClassFunction, "null");

    tuesdays = proxiedDayPicker.getSpecificDays(tuesdayDay);
    tuesdays.removeSpecificDays(DayType.boundaryDay);

    for (CalendarDay tuesday : tuesdays) {
      assertFalse(tuesday.containsStyleClass("yellowDay"), "All tuesdays should not be yellow.");
    }
  }