public void TestGetExchangeRate()
{
var stockExchange = new StockExchange();
stockExchange.AddExchangeRate(StockExchange.ExchangeRate(DateTime.Now, "CHF", "USD", 2.0M));
stockExchange.AddExchangeRate(StockExchange.ExchangeRate(DateTime.Now.AddMilliseconds(1d), "CHF", "USD", 2.1M));
var bank = new Bank(stockExchange, new MockUpCurrencyListing(), "USD");
var currentRate = stockExchange.GetExchangeRate("CHF", "USD");
Assert.AreEqual(currentRate.ConversionRate, 2.1M);
Assert.AreEqual(bank.GetInternalExchangeRate("CHF"), currentRate);
Assert.AreEqual(stockExchange.GetExchangeRate("CHF", "CAD"), null);
}