public void ShouldNotThrowException_WhenPayInLimitIsNotExceeded()
            {
                Account sut = new AccountBuilder().WithPaidIn(2000m);

                Assert.DoesNotThrow(() => { sut.EnsurePayInLimitIsNotExceeded(2000m); });
            }
            public void ShouldThrowException_WhenPayInLimitIsExceeded()
            {
                Account sut = new AccountBuilder().WithPaidIn(2000m);

                Assert.Throws <InvalidOperationException>(() => { sut.EnsurePayInLimitIsNotExceeded(3000m); });
            }