C# – Unit test for asynchronous code

cunit testingwindows-phone-8

I have got some code, which is using HttpWebRequest class's .BeginGetResponse() method and it is asynchronous. Also, I am using Microsoft's Unit Test App project for testing application.

The problem is that test framework does not waiting for end of running asynchronous code, so I can not check its result.

How should I test asynchronous code using Unit Test App project? I'm not using async/await modificators.

Best Answer

Update Answer
The original answer was quite an old one, before async and await were prevalent. I'd now recommend using them, by writing something like:

[TestMethod]
public async Task RunTest()
{
    var result = await doAsyncStuff();
    // Expectations
}

There's a good article that covers this in depth Async Programming : Unit Testing Asynchronous Code

Old Answer

I would tend to something simple like using a polling loop and checking a flag that would be set in the async code or you could use reset events. A simple example using threads:

[TestMethod]
public void RunTest()
{
    ManualResetEvent done = new ManualResetEvent(false);
    Thread thread = new Thread(delegate() {
        // Do some stuff
        done.Set();
    });
    thread.Start();

    done.WaitOne();
}

You'll need to think about exceptions and use a try/finally and report the errors to do this properly, but you get the idea. This method however might not suit if you're doing lots of async stuff over and over, unless you fancy pushing this into a reusable method.

Related Topic