Monday, July 21, 2008

Testing Mule applications

Antoine Borg has posted an intersting article at Ricston Blog about the feasibility of using mock objects for testing Mule applications. The bottom line is that in integration scenario is usually difficult to capture the application specification in mocks and often it's easier to write stub applications simulating the external systems (outside of your application process).

I've found that often I don't really test the whole application, but instead I test single components with a few attached transformers, filters and routers. I start by writing a simple Mule configuration - a single component using VM endpoints with queuing. Then I use MuleClient to feed in canned input data and assert the output from the outbound endpoint(s). As the application takes shape, I add transformers and routers as needed to approximate the real usage.

I could imagine that the next step would be to reuse my production configuration and extract the perimeter endpoint definitions in a new file (separating them from the model, connectors and internal endpoints) and pass the two configuration files to the config builder. This would allow me to create an alternative perimeter endpoints file using VM endpoints, so I can instantiate it in test case and use MuleClient for testing.

The benefits of the approach are that you are testing your component and routing logic and are not exposed to the peculiarities of the external system. Ideally we still want to have a full integration tests, including ones covering crash-failure, failover, connectivity loss and overload scenarios. We can achieve parts of this by stubbing the external system, but so far I usually find it difficult to reproduce the behaviour faithfully enough (especially when we have limited understanding about the external system).

No bulletpoints this time.

1 comment:

antoine said...

Hey Dimitar,

Thanks for reading!

You're right in suggesting that at times it makes sense to test single bits and pieces - that approach works well. if you're the type to write the tests before doing any coding or configuration, then the approach changes slightly of course - it's all a matter of what you're most comfortable with.

Best Regards

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