public void TestMakeChange()
        {
            //arrange
            Catering catering = new Catering(fa);

            //act
            catering.AddMoney("20");

            //Assert
            Assert.AreEqual("1 - Twenty", catering.MakeChange());

            //act
            catering.AddMoney("40");

            //Assert
            Assert.AreEqual("2 - Twenty", catering.MakeChange());

            //act
            catering.AddMoney("50");

            //Assert
            Assert.AreEqual("2 - Twenty, 1 - Ten", catering.MakeChange());
        }