@Test
    public void twoInchPlusTwoInchEqualFourInch(){
        ArithmeticQuantity two_inches = new ArithmeticQuantity(2, Distance.INCHES);
        ArithmeticQuantity two_inches2 = new ArithmeticQuantity(2, Distance.INCHES);

        assertEquals(new ArithmeticQuantity(4, Distance.INCHES), two_inches.add(two_inches2));

    }