public void ShouldReduceBalance()
            {
                Account sut = new AccountBuilder().WithBalance(1000m);

                sut.Debit(250m);

                var expected = 750m;

                Assert.AreEqual(expected, sut.Balance);
            }
            public void ShouldReduceWithdrawn()
            {
                Account sut = new AccountBuilder().WithWithdrawn(0m);

                sut.Debit(250m);

                var expected = -250m;

                Assert.AreEqual(expected, sut.Withdrawn);
            }