Why doesn't NetMQ work in an NUnit environment

Question

I've created a Gist with my NetMQ implementation as I feel it a bit much to paste here: https://gist.github.com/gthvidsten/e626d7e6c51012b1ba152d22e034d93d

If I do the following in a .Net Core console app, everything works fine and I receive the MessageReceived event:

static void Main(string[] args)
{
    _transportWithHost = new NetMqTransport(
        "tcp://localhost:9990",
        "tcp://localhost:9991",
        true);
    _transportWithHost.Start();

    Console.WriteLine("Press [Enter] to publish");
    Console.ReadLine();

    _transportWithHost.MessageReceived += (sender, e) =>
    {
        ; // Breakpoints here are hit
    };
    _transportWithHost.Publish(new byte[] { 1, 2, 3, 4 });

    Console.WriteLine("Press [Enter] to exit");
    Console.ReadLine();
}

However, if I try to do the same in an NUnit test environment, the MessageReceived event is never fired!

class NetMqTransportTests
{
    private NetMqTransport _transportWithHost;

    [OneTimeSetUp]
    public void Setup()
    {
        _transportWithHost = new NetMqTransport(
            "tcp://localhost:9990",
            "tcp://localhost:9991",
            true);
        _transportWithHost.Start();
    }

    [Test]
    public void PublishTest()
    {
        ManualResetEvent mre = new ManualResetEvent(false);

        _transportWithHost.MessageReceived += (sender, e) =>
        {
            mre.Set();
            // Breakpoints here are never hit as MessageReceived is never called
        };

        _transportWithHost.Publish(new byte[] { 1, 2, 3, 4 });

        bool eventFired = mre.WaitOne(new TimeSpan(0, 0, 5));
        Assert.True(eventFired);
    }
}

Why does the virtually identical code work in a console app, but not in an NUnit environment?

Jeremy Thompson · Answer 1 · 2019-07-18T06:27:40.867

I was able to reproduce it and found this thread https://github.com/zeromq/netmq/issues/482 which indicates its a timing issue between starting the Publisher and time for the Subscriber to receive the message.

using NetMQ;
using NetMQ.Sockets;
using NUnit.Framework;
using System;
using System.Threading;
using System.Threading.Tasks;

namespace Tests
{
    class NetMqTransportTests
    {
        [Test]
        public void TestMulticastNetMQ()
        {
            bool wasCalled = false;

            var coreEventbus = "tcp://localhost:12345";

            Task.Run(() =>
            {
                using (var subSocket = new SubscriberSocket())
                {
                    subSocket.Connect(coreEventbus);
                    subSocket.Subscribe("account");

                    while (true)
                    {
                        string messageTopicReceived = subSocket.ReceiveFrameString();
                        string messageReceived = subSocket.ReceiveFrameString();

                        Assert.IsTrue(messageReceived == "testing");
                        wasCalled = true;
                        break;
                    }
                }

            });

            Thread.Sleep(TimeSpan.FromSeconds(1));

            using (var pubSocket = new PublisherSocket())
            {
                pubSocket.Bind(coreEventbus);

                Thread.Sleep(500);
                pubSocket.SendMoreFrame("account").SendFrame("testing");
            }

            Thread.Sleep(TimeSpan.FromSeconds(5));

            Assert.IsTrue(wasCalled);
        }
    }
}

Update:

Here are the Unit Tests that come with the NetMQ library: https://github.com/zeromq/netmq/blob/master/src/NetMQ.Tests/XPubSubTests.cs

See how they break up instantiating NetMqTransport into using both XPublisherSocket and XPublisherSocket...

Also notice as per the issue 482 they do a 500ms delay to let the subscriber connect before receiving the message, just like they were talking about in the issue:

[Fact]
public void TopicPubSub()
{
    using (var pub = new XPublisherSocket())
    using (var sub = new XPublisherSocket())
    {
        var port = pub.BindRandomPort("tcp://127.0.0.1");
        sub.Connect("tcp://127.0.0.1:" + port);
        sub.SendFrame(new byte[] { 1, (byte)'A' });

        // let the subscriber connect to the publisher before sending a message
        Thread.Sleep(500);

        var msg = pub.ReceiveFrameBytes();

See update - they are unit testing their framework. So while you should code in a smoke test and an integration don't bother double unit testing!! I'm not going to go into the philosophy of unit testing vs integration testing but generally in unit testing you don't test external resources instead we mock/stub them, especially when its a 3rd party component that has its own regression testing suite. — Jeremy Thompson, Jul 17 '19 at 23:38
So a 500ms delay every time I do `NetMqTransport.Start()` should be enough to fix everything then? (I tried it and it seems to help, but would be nice to have a confirmation that it is correct... also, a `Thread.Sleep` feels a bit dirty. I tried with a ResetEvent, but this caused a deadlock somewhere.) — TheHvidsten, Jul 18 '19 at 14:18
I'm still wondering why they dont have any Unit Test for the `NetMqTransport`, I might add to your GitHub ticket to politely raise a bit more awareness. — Jeremy Thompson, Jul 19 '19 at 02:59
The `NetMqTransport.Start()` is a part of my code and not NetMQ (it can be found in `NetMQ.cs` in the Gist), which is probably why you can't find any Unit Tests for it :) — TheHvidsten, Jul 19 '19 at 08:01

Why doesn't NetMQ work in an NUnit environment

1 Answers1