public void SubscriberTest()
{
Market market = new Market(new string[] { "Apple", "Google" });
var mock = new Mock <ISubscriber>();
mock.Setup(foo => foo.Notified(market, It.IsAny <MarketEventArgs>()));
market.AddSubscriber(mock.Object);
market.Trade();
mock.Verify(r => r.Notified(market, It.IsAny <MarketEventArgs>()));
}