public void CanAddCurrency()
        {
            var mock = new Mock<ICurrencyRepository>();
            mock.Setup(c => c.GetCurrencies()).Returns(new List<Currency>
            {
                new Currency {Id = 1, Name="USD", ShortName = "United States Dollar", Symbol = "$"},
            });

            var currency1 = new Currency { Id = 2, Name = "ETH", ShortName = "Ethereum", Symbol = "Ξ" };
            var currency2 = new Currency { Id = 3, Name = "BTC", ShortName = "Bitcoin", Symbol = "฿" };

            mock.Object.RegisterNewCurrency(currency1);
            mock.Object.RegisterNewCurrency(currency2);

            var list = mock.Object.GetCurrencies();

            Assert.AreEqual(list.Count, 3);
            Assert.AreEqual(list[1].Id, currency1.Id);
            Assert.AreEqual(list[2].Id, currency2.Id);
        }