Simple IConsume<T> unit test with a mock

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Jens Pettersson

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Apr 27, 2016, 10:34:29 AM4/27/16
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Hello. I'm new to MassTransit and are currently exploring the possibility to unit test a consumer. The test scenario is as follows: 
  • A consumer receives a message that tells it to handle a product registration
  • The consumer should store the registration request in some kind of storage
The consumer has a dependency to an interface and all I want to do is to assert that the interface gets called. Terribly simple, but I fail to understand what type of Mass Transit test I should build for this simple scenario. After browsing the MT code base and looking at the unit tests there, this is what I came up with:

[TestFixture]
public class LabTests : InMemoryTestFixture
{
private IHandleProduct _handleProduct;

[SetUp]
public async void SetUp()
{
_handleProduct = A.Fake<IHandleProduct>();
await InputQueueSendEndpoint.Send<IRegisterProduct>(new { ProductId = "product-id"});
}

[Test]
public void Should_call_product_handler()
{
_handleProduct.CallsTo(x => x.Handle("product-id")).MustHaveHappened();
}

protected override void ConfigureInputQueueEndpoint(IInMemoryReceiveEndpointConfigurator configurator)
{
configurator.Consumer(() => new RegisterProductConsumer(_handleProduct));
}
}

This works... but not all the time. I assume this is due to the async nature of Mass Transit...

I can just try to test the consumer directly (i.e. no InMemoryTestFixture) but then I have to pass in a ConsumerContext<T> in the Consume(...) method. I can stub that as well, but it seems like a hack. 

The consume method is nothing more than this:

public Task Consume(ConsumeContext<IRegisterProduct> context)
{
//not async...
_handler.Handle(context.Message.ProductId);

return context.CompleteTask;
}

I might be missing something super simple here, and it bugs me. Probably something async related... Any ideas?

Thanks!

//J

Chris Patterson

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Apr 27, 2016, 11:13:03 AM4/27/16
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The setup method cannot be async as NUnit doesn't support it. That's likely why it's unpredictable. 

__
Chris Patterson




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Jens Pettersson

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Apr 27, 2016, 11:23:45 AM4/27/16
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Oh, I hope it's that simple. Will test when I get back to my client tomorrow.

I'm curious if that kind of test (the InMemoryTestFixture) is a preferred way of testing simple things like this or if there are other, more recommended, ways of doing it?

Thanks for the reply Chris!

//J
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Chris Patterson

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Apr 27, 2016, 3:38:48 PM4/27/16
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The InMemoryTestFixture is the best way to test consumers, since it does a full end-to-end test of the message, serialization, consumer, etc.


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Jens Pettersson

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Apr 27, 2016, 4:43:18 PM4/27/16
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Thank you, Chris. Much appreciated!
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Marko Lahma

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Apr 28, 2016, 1:18:49 AM4/28/16
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Jens,

I recommend upgrading to NUnit 3 if possible when testing async code, it has scenarios better covered. https://github.com/nunit/docs/wiki/SetUp-Attribute : "SetUp methods may be async if running under .NET 4.0 or higher.". You can even get old NUnit 2 style XML output with a switch from console runner to keep builder servers happy.

And I also recommend creating a test that checks that there is no async void methods :)


Cheers,
Marko
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Jens Pettersson

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Apr 28, 2016, 2:36:38 AM4/28/16
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Thank you Marko.

Alltough, I'm having a hard time running an 'InMemoryTestFixture' with NUnit3 and ReSharper (2016.1). The test just dissappears from the runner. Anyone know if the TestFramework for Mass Transit has issues with Nunit 3? The InMemoryTestFixture doesn't get picked up by the nunit3-console.exe runner for me as well :/

Sudhanshu Mishra

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Apr 28, 2016, 2:46:00 AM4/28/16
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Hi Jens,

From prior experience, ReSharper test runner does not like versions of NUnit prior to NUnit 3. If the MassTransit framework uses a lower version of NUnit, that may be the reason for tests to disappear.
You should still see the tests in the Test Explorer though..
cheers
Sud

Jens Pettersson

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Apr 28, 2016, 3:08:54 AM4/28/16
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Just an update, I downgraded to NUnit 2.6.4 as we're using it everywhere else (for example, the Akka.NET TestKit didn't support NUnit 3.x last time I checked and we're using it quite a bit in some of our projects). I changed the test to not use async in a setup (actually removed the setup completely in favour for a TestFixtureSetUp) and now the test works great. Every time.

Thanks for all the help guys. I appreciate it!

//J

Marko Lahma

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Apr 28, 2016, 3:12:13 AM4/28/16
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Unfortunately I'm not currently using InMemoryTestFixture, I've just picked some parts from test framework library without using the actual test cases / base classes. A quick and dirty way might be copy-pasting the InMemoryTestFixture as CustomInMemoryTestFixture to your code base and check whether it works better when it's targeted directly against your NUnit 3 version.

-Marko
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