public void CheckBalance_RequestsTheAccountBalanceFromTheRepository()
        {
            const int nonZeroBalance = 1;

            Mock.Get(_accountRepository).Setup(x => x.GetBalance())
            .Returns(nonZeroBalance);

            var balance = _teller.CheckBalance();

            Assert.That(balance, Is.EqualTo(nonZeroBalance), "Checking the balance should return the balance retrived from the repository.");
        }