如何测试事件是否包含事件处理程序？

Question

我想测试该类A的{​​{1}}方法将其方法之一注册为RegisterEventHandlers()，用于类EventHandler上的事件。我怎样才能做到这一点？如果重要的话，我正在使用moq。

• 我认为没有办法从课外检查事件处理程序委托（如果我错了请纠正我）。
• 如果我可以触发事件然后断言我的回调被调用，那将是很好的，但如果我模拟B类的接口（并设置回调的期望），那么我输了A的实现，这是我首先测试的方法。
• 模拟RegisterEventHandlers()类的事件将是最好的选择，但我不知道有什么方法可以拦截这样做。有没有办法为事件设置模拟，并拦截B方法调用？

这有一个干净的解决方案吗？

Answer 1

在模拟B时，像这样声明EventHandler：

public class B : IB
{
  public int EventsRegistered;
  public event EventHandler Junk
  {
     add
     {
        this.EventsRegistered++;
     }
     remove
     {
        this.EventsRegistered--;
     }
  }
}

我不确定moq允许这样做，但我相信你可以创建自己的模拟类。

Answer 2

你是不对的，你不能从课外访问事件代理，这是C＃语言的限制。

最直接的测试方法是模拟B类，然后提升它的事件，然后观察被引发事件的副作用。这与您正在寻找的略有不同，但它演示了类的A行为而不是它的实现（这是您的测试应该努力做的事情）。

为了使其工作，B类必须是可模拟的，并且它公开的事件也必须是虚拟的。如果事件未被声明为虚拟，则Moq无法拦截事件。或者，如果B是接口，请确保在那里声明事件。

public interface IEventProvider
{
    event EventHandler OnEvent;
}

public class Example
{
    public Example(IEventProvider e)
    {
        e.OnEvent += PerformWork;
    }

    private void PerformWork(object sender, EventArgs e)
    {
        // perform work

        // event has an impact on this class that can be observed
        //   from the outside.  this is just an example...
        VisibleSideEffect = true;
    }

    public bool VisibleSideEffect
    {
       get; set;
    }
}

[TestClass]
public class ExampleFixture
{
    [TestMethod]
    public void DemonstrateThatTheClassRespondsToEvents()
    {
        var eventProvider = new Mock<IEventProvider>().Object;
        var subject = new Example(eventProvider.Object);

        Mock.Get(eventProvider)
            .Raise( e => e.OnEvent += null, EventArgs.Empty);

        Assert.IsTrue( subject.VisibleSideEffect, 
                       "the visible side effect of the event was not raised.");
    }
}

如果确实需要测试实现，则还有其他可用的机制，例如手动Test Spy / Test Double或基于反射的策略来获取委托列表。我希望你应该更关注A类的事件处理逻辑而不是它的事件处理程序赋值。毕竟，如果A类没有对事件做出回应并对事件采取措施，那么任务就不重要了。

Answer 3

您可以获取声明事件的类之外的事件的调用列表 - 但它涉及反射。下面是一个代码示例，说明如何在调用 a.RegisterEventHandlers后确定哪些方法（在目标实例 a 上）添加到事件 b .Event （）即可。将下面的代码粘贴到代码文件中并添加到表单或控制台项目中：测试test = new Test（）; test.Run（）;

using System;
using System.Reflection;
using System.Diagnostics;
using System.Collections.Generic;

   public class A
   {
      B m_b = new B();

      public void RegisterEventHandlers()
      {
         m_b.TheEvent += new EventHandler(Handler_TheEvent);
         m_b.TheEvent += new EventHandler(AnotherHandler_TheEvent);
      }

      public A()
      { 
         m_b.TheEvent += new EventHandler(InitialHandler_TheEvent);
      }

      void InitialHandler_TheEvent(object sender, EventArgs e)
      { }

      void Handler_TheEvent(object sender, EventArgs e)
      { }

      void AnotherHandler_TheEvent(object sender, EventArgs e)
      { }
   }

   public class B
   {
      public event EventHandler TheEvent;
      //{
      //   //Note that if we declared TheEvent without the add/remove methods, the
      //   //following would still generated internally and the underlying member
      //   //(here m_theEvent) can be accessed via Reflection. The automatically
      //   //generated version has a private field with the same name as the event
      //   //(i.e. "TheEvent")

      //   add { m_theEvent += value; }
      //   remove { m_theEvent -= value; }
      //}
      //EventHandler m_theEvent; //"TheEvent" if we don't implement add/remove


      //The following shows how the event can be invoked using the underlying multicast delegate.
      //We use this knowledge when invoking via reflection (of course, normally we just write
      //if (TheEvent != null) TheEvent(this, EventArgs.Empty)
      public void ExampleInvokeTheEvent()
      {
         Delegate[] dels = TheEvent.GetInvocationList();
         foreach (Delegate del in dels)
         {
            MethodInfo method = del.Method;
            //This does the same as ThisEvent(this, EventArgs.Empty) for a single registered target
            method.Invoke(this, new object[] { EventArgs.Empty });
         }
      }
   }


   public class Test
   {
      List<Delegate> FindRegisteredDelegates(A instanceRegisteringEvents, B instanceWithEventHandler, string sEventName)
      {
         A a = instanceRegisteringEvents;
         B b = instanceWithEventHandler;

         //Lets assume that we know that we are looking for a private instance field with name sEventName ("TheEvent"), 
         //i.e the event handler does not implement add/remove.
         //(otherwise we would need more reflection to determine what we are looking for)
         BindingFlags filter = BindingFlags.Instance | BindingFlags.NonPublic;

         //Lets assume that TheEvent does not implement the add and remove methods, in which case
         //the name of the relevant field is just the same as the event itself
         string sName = sEventName; //("TheEvent")

         FieldInfo fieldTheEvent = b.GetType().GetField(sName, filter);

         //The field that we get has type EventHandler and can be invoked as in ExampleInvokeTheEvent
         EventHandler eh = (EventHandler)fieldTheEvent.GetValue(b);

         //If the event handler is null then nobody has registered with it yet (just return an empty list)
         if (eh == null) return new List<Delegate>();


         List<Delegate> dels = new List<Delegate>(eh.GetInvocationList());

         //Only return those elements in the invokation list whose target is a.
         return dels.FindAll(delegate(Delegate del) { return Object.ReferenceEquals(del.Target, a); });
      }

      public void Run()
      {
         A a = new A();

         //We would need to check the set of delegates returned before we call this

         //Lets assume we know how to find the all instances of B that A has registered with
         //For know, lets assume there is just one in the field m_b of A.
         FieldInfo fieldB = a.GetType().GetField("m_b", BindingFlags.Instance | BindingFlags.NonPublic);
         B b = (B)fieldB.GetValue(a);

         //Now we can find out how many times a.RegisterEventHandlers is registered with b
         List<Delegate> delsBefore = FindRegisteredDelegates(a, b, "TheEvent");

         a.RegisterEventHandlers();

         List<Delegate> delsAfter = FindRegisteredDelegates(a, b, "TheEvent");

         List<Delegate> delsAdded = new List<Delegate>();
         foreach (Delegate delAfter in delsAfter)
         {
            bool inBefore = false;
            foreach (Delegate delBefore in delsBefore)
            {
               if ((delBefore.Method == delAfter.Method)
                  && (Object.ReferenceEquals(delBefore.Target, delAfter.Target)))
               {
                  //NOTE: The check for Object.ReferenceEquals(delBefore.Target, delAfter.Target) above is not necessary 
                  //     here since we defined FindRegisteredDelegates to only return those for which .Taget == a)

                  inBefore = true;
                  break;
               }
            }
            if (!inBefore) delsAdded.Add(delAfter);
         }

         Debug.WriteLine("Handlers added to b.TheEvent in a.RegisterEventHandlers:");
         foreach (Delegate del in delsAdded)
         {
            Debug.WriteLine(del.Method.Name);
         }


      }
   }

Answer 4

我对单元测试知之甚少，但也许this link可以给你一些想法。请注意，virtual关键字也适用于此处。

Answer 5

我认为moq不具备这种能力 - 如果您准备购买工具我建议您使用Typemock Isolator来验证对象上的任何方法都被调用 - 包括事件处理程序 - 有一个{ {3}}