[rspec-users] Writing specs for AMQP clients.

Ben Mabey ben at benmabey.com
Wed Mar 4 11:27:20 EST 2009


David Chelimsky wrote:
> On Wed, Mar 4, 2009 at 4:54 AM, Bira <u.alberton at gmail.com> wrote:
>   
>> Hello!
>>
>> I've been lurking in the list a while, and now I would like to ask you
>> a somewhat "noobish" question... This is the first time I've run
>> across this particular problem, so I'm not sure what to do. I'm sure
>> this is so common that's in a textbook somewhere, but what is the best
>> way to write specs for code that calls out to an external server?
>>
>> I've just started working on a project that will use AMQP messaging
>> (and the "amqp" gem), and most of the code I've written so far is all
>> about talking to a messaging server. The only alternatives I saw for
>> writing specs were starting said server, and mocking/stubbing out all
>> the code that would talk to it. I went witht he second one, but I feel
>> it's a fragile approach that won't actually allow me to find bugs,
>> since everything is mocked out. What is the best way to do this?
>>     
>
> I'm not familiar w/ amqp in particular, but one "good" approach is to
> use mock objects to evolve a protocol for this service in the language
> of your app, and then write an adapter for amqp with a few system
> level tests in place to verify happy paths.
>
> This approach does a few good things.
>
> * Keeps you focused on the business domain while writing the business
> objects, because you're not sidetracked by the details of messaging.
> * Keeps the suite of specs running fast
> * Makes it easy to choose a different messaging API later, because all
> of the code that depends directly on that API lives in the adapter.
>
> HTH,
> David
>
>
>   

Bria,
In the past, I have done exactly as David has suggested.  I have my 
cucumber features use the actual messaging system to verify that 
everything is hooked up and is working correctly.  I then use a 
combination of null and fake adapters in my specs to keep them fast and 
focused on testing the object's responsibility.  Doing this required 
that an adapter layer be introduced.  The nice thing about this, as 
David also points out, is that you can then easily swap out another 
messaging system by simply writing a new adapter.

I have actually open soured my efforts (and my coworker's, Chris 
Wyckoff) so you can use, or at least get ideas from, the library here:

https://github.com/bmabey/rosetta_queue/tree

You can use currently use the library with messaging systems that speak 
AMQP or stomp.

Additionally, I have blogged about how we used Cucumber and this library 
to integrate our distributed systems:

http://www.benmabey.com/2009/02/17/using-cucumber-to-integrate-distributed-systems-and-test-messaging/

HTH,
Ben




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