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Writing Unit or Integration Tests That Rely on Events Firing

Posted by Keith Elder | Posted in .Net, C# | Posted on 22-10-2010

For the past week or so I’ve been working on wrapping the Sonic API to simplify it for developers at my company.  The API itself is pretty much a straight port from Java.  There is nothing C# about the API.  For example no enumerations, no generics, no nothing.  This means when you are using the API you see functions that take a parameter that is just an integer since there are no enumerations for example.  That wouldn’t be so bad if the code was documented in the proper C# way but it isn’t.  So, instead of having 100+ developers at work learn how Sonic works I have been coding up several scenarios that we need to support for the business. 

In my quest to wrap the Sonic API into a more C# centric approach I needed to write some tests obviously to make sure things were working.  Primarily these are integration tests as each test relies upon connecting to a Sonic dev environment. 

If you aren’t familiar with Sonic it is an enterprise messaging platform.  It does pub/sub, supports queues, fault tolerate and so on.  I think the stock market even uses Sonic to route messages so it has a proven track record. 

One of the scenarios I had to cover was I needed to send a message to a queue and then have that message pulled out of the queue on the other side, processed and acknowledged.  In order to do this there is one object that sends a message, and another object that is listening for a message(s).   But how do you write a test that waits on an event to happen?  Well, it turns out we’d done this before in other tests but I couldn’t for the life of me remember how.  So here’s how it works. 

Using an EventWaitHandle we can wait on an event to occur.  First is to create a handle.

   1: EventWaitHandle handle = new ManualResetEvent(false);

Using the handle we can tell it to WaitOne() which blocks the current thread until the WaitHandle receives a signal.

   1: handle.WaitOne();

Then inside our event we simply call handle.Set() (this is the signal). 

Putting all of this together we can write an integration test that sends a message to Sonic and then waits for that message to come through.  Obviously the Sonic piece doesn’t really matter, the important piece here is how to get a test to wait for an event.  Putting it all together it looks like this.

   1: [TestMethod]

   2: public void Can_Send_To_Queue_And_Receive_Message_From_Queue()

   3: {

   4:     EventWaitHandle handle = new ManualResetEvent(false);

   5:     SonicQueueSender sender = new SonicQueueSender(Helpers.SonicQueueArgs);

   6:     string sendMsg = "test";

   7:     sender.SendMessage(sendMsg, SonicDeliveryMode.NonPersistent);

   8:     SonicQueueReceiver consumer = new SonicQueueReceiver(Helpers.SonicQueueArgs);

   9:     string receiveMsg = "";

  10:     consumer.MessageRecieved += (mySender, args) =>

  11:         {

  12:             TextMessage txtMsg = (TextMessage)args.Message;

  13:             receiveMsg = txtMsg.getText();

  14:             handle.Set();

  15:         };

  16:     consumer.StartListener();

  17:     handle.WaitOne();

  18:     Assert.AreEqual(receiveMsg, sendMsg);

  19: }

Hope this helps someone out.

  • Thanks for this! is very nice information, cooll!!