Using Rx to help Async testing

RxAsyncTesting.cs

// The class under test (a "device") has one background thread which monitors the (fake) serial port for incoming
// data and places it on a queue for a second background thread to pickup, process and respond to. 
//
// Normally I'd have to test this with Thread.Sleep, which is not only ugly, but also slows down every test as the
// sleep time would have to be long enough so machines under heavy load didn't fail.
//
// With Rx I can setup an observable on my fake serial port "Data Written" event and tell it to wait up to 5 seconds
// to receive and event of the correct type. Then I can simply pull those chunks of data out of the enumerable
// it produces and assert on them as normal.
//
// Other than a little bit of Rx plumbing the test is pretty much the same as a non-async test would be, and still
// remains quite readable.
[TestMethod]
public void Device_Sends_Login_Confirm_Message_When_Handset_Sends_Login_Request_Message()
{
    var inputBytes = (byte[])(new HardwareMessage(MessageType.LoginRequest, 1, new Parameters()
        {
            Parameter0 = 1,
            Parameter1 = 2,
            Parameter2 = 3,
        }));
    var dataWritten = (from evt in Observable.FromEvent<DataWrittenEventArgs>(_SerialPort, "DataWritten")
                       where ((HardwareMessage)evt.EventArgs.Data).MessageType == MessageType.ConfirmLogin
                       select evt.EventArgs.Data).Take(1).Timeout(new TimeSpan(0, 0, 5));

    _SerialPort.Buffer = inputBytes;

    var output = dataWritten.ToEnumerable().ToArray();
    var hardwareMessage = (HardwareMessage)output[0];
    Assert.AreEqual(MessageType.ConfirmLogin, hardwareMessage.MessageType); // Do any assertions required
}