@Test
    public void twoTablespoonPlusOneOunceEqualTwelveTeaspoon(){

        ArithmeticQuantity two_tbsp = new ArithmeticQuantity(2, Volume.TABLESPOON);
        ArithmeticQuantity one_oz = new ArithmeticQuantity(1, Volume.OUNCE);
        assertEquals(two_tbsp.add(one_oz), new ArithmeticQuantity(12, Volume.TEASPOON));
    }