public void SerializeBankTransferToXml()
 {
     var payer = new BankAccount(accountNumber: "1", amount: 1.0);
     var payee = new BankAccount(accountNumber: "2", amount: 0.0);
     var sut = new BankTransfer(payer, payee, amount: 1.0);
     var xml = sut.ToXml();
     Assert.That(xml, Is.StringContaining(payer.GetAccountNumber()), "payer accountnumber");
     Assert.That(xml, Is.StringContaining(payee.GetAccountNumber()), "payee accountnumber");
     Assert.That(xml, Is.StringContaining("1.0"), "amount");
 }