[Silverlight入门系列]Prism的事件EventAggregator如何单元测试UnitTesting

时间：2011-06-07 来源：Mainz

上一篇说了如何进行Prism和MEF的单元测试，今天来说一下Prism中的事件发布和订阅EventAggregator如何进行测试？大家知道在Prism中可用EventAggregator:

using Microsoft.Practices.Prism.Events;
        
private IEventAggregator TheEventAggregator { get; set; }
        
[ImportingConstructor]
public MyViewModel(IEventAggregator eventAggregator)
{
    TheEventAggregator = eventAggregator;
    //TODO: 
}

然后可以进行事件的发布（Publish）和订阅（Subscribe）：

TheEventAggregator.GetEvent<MarketPricesUpdatedEvent>().Publish(clonedPriceList);

上面代码中用到了一个自定义的Event: MarketPriceUpdatedEvent: （定义成你需要的数据类型就可以了，这里是IDictionary<string, decimal>）

public class MarketPricesUpdatedEvent : CompositePresentationEvent<IDictionary<string, decimal>>
{
}

如果一个函数最后一行是发布一个事件，没有返回值，如何对它进行单元测试？如何测试这个事件已经Publish了呢？

我们可以自己写一个Mock的EventAggregator：

class MockEventAggregator : IEventAggregator
{
    Dictionary<Type, object> events = new Dictionary<Type, object>();
    public TEventType GetEvent<TEventType>() where TEventType : EventBase, new()
    {
        return (TEventType)events[typeof(TEventType)];
    }

    public void AddMapping<TEventType>(TEventType mockEvent)
    {
        events.Add(typeof(TEventType), mockEvent);
    }
}

class MockPriceUpdatedEventAggregator : MockEventAggregator
{
    public MockMarketPricesUpdatedEvent MockMarketPriceUpdatedEvent = new MockMarketPricesUpdatedEvent();
    public MockPriceUpdatedEventAggregator()
    {
        //注意这个不是Mock的，是原来的！
        AddMapping<MarketPricesUpdatedEvent>(MockMarketPriceUpdatedEvent);
    }

    public class MockMarketPricesUpdatedEvent : MarketPricesUpdatedEvent
    {
        public bool PublishCalled;
        public IDictionary<string, decimal> PublishArgumentPayload;
        public EventHandler PublishCalledEvent;

        private void OnPublishCalledEvent(object sender, EventArgs args)
        {
            if (PublishCalledEvent != null)
                PublishCalledEvent(sender, args);
        }

        public override void Publish(IDictionary<string, decimal> payload)
        {
            PublishCalled = true;
            PublishArgumentPayload = payload;
            OnPublishCalledEvent(this, EventArgs.Empty);
        }
    }
}

然后在单元测试类里面就可以用这个mock的事件了：

[TestMethod]
public void TestPublishedEvent()
{
    var eventAgregator = new MockPriceUpdatedEventAggregator();
    var marketFeed = new TestableMarketFeedService(eventAgregator);
    Assert.IsTrue(marketFeed.SymbolExists("STOCK0"));

    marketFeed.InvokeUpdatePrices();
    
    //验证事件发布
    Assert.IsTrue(eventAgregator.MockMarketPriceUpdatedEvent.PublishCalled);
    
    //验证事件的参数
    var payload = eventAgregator.MockMarketPriceUpdatedEvent.PublishArgumentPayload;
    Assert.IsNotNull(payload);
    Assert.IsTrue(payload.ContainsKey("STOCK0"));
    Assert.AreEqual(marketFeed.GetPrice("STOCK0"), payload["STOCK0"]);
}