public void When_TickProvided_Then_MarketListenerReceiveTickEvent() { // setup var moq = new Mock <IMarketListener>(); market.Subscribe(moq.Object); // when tick provided var tick = Tick.ForNow(100, 99); tickProvider.Raise(m => m.Tick += null, new TickEventArgs(tick)); // then market listener should receive tick moq.Verify(m => m.OnTick(It.IsAny <Tick>()), Times.Once); }