Opening seams for testing

time to read 14 min | 2722 words

While testing Rhino Service Bus, I run into several pretty annoying issues. The most consistent one is that the actual work done by the bus is done on another thread, so we have to have some synchronization mechanisms build into the bus just so we would be able to get consistent tests.

In some tests, this is not really needed, because I can utilize the existing synchronization primitives in the platform. Here is a good example of that:

   1: [Fact]
   2: public void when_start_load_balancer_that_has_secondary_will_start_sending_heartbeats_to_secondary()
   3: {
   4:     using (var loadBalancer = container.Resolve<MsmqLoadBalancer>())
   5:     {
   6:         loadBalancer.Start();
   8:         Message peek = testQueue2.Peek();
   9:         object[] msgs = container.Resolve<IMessageSerializer>().Deserialize(peek.BodyStream);
  11:         Assert.IsType<HeartBeat>(msgs[0]);
  12:         var beat = (HeartBeat)msgs[0];
  13:         Assert.Equal(loadBalancer.Endpoint.Uri, beat.From);
  14:     }
  15: }

Here, the synchronization is happening in line 8, Peek() will wait until a message arrive in the queue, so we don’t need to manage that ourselves.

This is not always possible, however, and this actually breaks down for more complex cases. For example, let us inspect this test:

   1: [Fact]
   2: public void Can_ReRoute_messages()
   3: {
   4:     using (var bus = container.Resolve<IStartableServiceBus>())
   5:     {
   6:         bus.Start();
   7:         var endpointRouter = container.Resolve<IEndpointRouter>();
   8:         var original = new Uri("msmq://foo/original");
  10:         var routedEndpoint = endpointRouter.GetRoutedEndpoint(original);
  11:         Assert.Equal(original, routedEndpoint.Uri);
  13:         var wait = new ManualResetEvent(false);
  14:         bus.ReroutedEndpoint += x => wait.Set();
  16:         var newEndPoint = new Uri("msmq://new/endpoint");
  17:         bus.Send(bus.Endpoint,
  18:                  new Reroute
  19:                  {
  20:                      OriginalEndPoint = original,
  21:                      NewEndPoint = newEndPoint
  22:                  });
  24:         wait.WaitOne();
  25:         routedEndpoint = endpointRouter.GetRoutedEndpoint(original);
  26:         Assert.Equal(newEndPoint, routedEndpoint.Uri);
  27:     }
  28: }

Notice that we are making explicit synchronization in the tests, line 14 and line 24. ReroutedEndpoint is an event that we added for the express purpose of allowing us to write this test.

I remember several years ago the big debates on whatever it is okay to change your code to make it more testable. I haven’t heard this issue raised in a while, I guess that the argument was decided.

As a side note, in order to get rerouting to work, we had to change the way that Rhino Service Bus viewed endpoints. That was a very invasive change, and we did it in less than two hours, but simply making the change and fixing the tests where they broke.