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Behaviour-Driven Design

09 Oct 2006 . tech . Comments #tdd #ddd #bdd

Finally some time to talk about my most recent pet pieve. Rest assured, the message is just the same as with my rants on Test-Driven Development. But as Dan says: It’s all about getting the words right. Dan has gotten this impulse from Domain Driven Design, and you all should know how I feel about that.

So what is the core message: TDD is not about testing, it’s all about behaviour!!! Behaviour-Driven Design helps us put the right focus on unit testing. Is this really any different from TDD? Well, not if you do it right. The problem is that the right way to do TDD is often hidden by the word Test. Many people think the main benefit of Test-Driven Design is testing your code, which is natural with this name.


The most important benefit of TDD is that it drives the design, the behaviour of your code. This is what BDD helps point out. BDD is an extension of TDD and Acceptance-Test Driven Planning. Basically it gives a template to use when defining User stories, that includes a context for the story, a benefit that the feature will give and a set of scenarios that can be used for acceptance tests.

For me this puts a required frame around the whole concept of developing quality code. There needs to be a connection between the story with its acceptance criteria, and the tests that we write for the code.

JBehave is a testing framwork that tries to make it easier to write tests the way the should be written. Its Ruby cousin is rBehave (the site is not operational yet, coming soon). I haven’t had the chance to try them out yet, so the code will have to wait until another time. Be sure to check it out.