public void testPlus_Months() {
        Months test2 = Months.months(2);
        Months test3 = Months.months(3);
        Months result = test2.plus(test3);
        assertEquals(2, test2.getMonths());
        assertEquals(3, test3.getMonths());
        assertEquals(5, result.getMonths());
        
        assertEquals(1, Months.ONE.plus(Months.ZERO).getMonths());
        assertEquals(1, Months.ONE.plus((Months) null).getMonths());
        
        try {
            Months.MAX_VALUE.plus(Months.ONE);
            fail();
        } catch (ArithmeticException ex) {
            // expected
        }
    }