public void Open() { var mockOpenedHandler = new Mock <OnOpened>(); var processor = new EngineIOProtocolProcessor(); processor.Process(new MessageContext { Message = "0{\"sid\":\"6lV4Ef7YOyGF-5dCBvKy\",\"upgrades\":[],\"pingInterval\":10000,\"pingTimeout\":5000}", OpenedHandler = mockOpenedHandler.Object }); Assert.AreEqual(typeof(OpenedProcessor), processor.NextProcessor.GetType()); mockOpenedHandler.Verify(x => x(It.IsAny <string>(), It.IsAny <int>(), It.IsAny <int>()), Times.Once()); }