Behaviour Driven Development

Recently there has been quite a bit of fuss about Behaviour Driven Development. So, what is it all about? You should have a look at that presentation from Dave Astels, it is quite interesting:

Presentation: “Beyond Test Driven Development: Behaviour Driven Development”

You can also view and download the video here.

What this is about?

In short, Behaviour Driven Development can be summarized into just one sentence:

Behaviour Driven Development is exactly what you are doing if you do Test Driven Development right.

That’s it? Yep, that’s it. Test driven Development is truely excellent in theory, but in practice it takes a long time to master. The people behind Behaviour Driven Development argue that this is due to bad naming. Language strongly influences how you think, and when you develop test-driven, you constantly talk about “tests”, “units”, “asserts” etc. If you are unexperienced this puts you in a wrong mindstate, because TDD it is not so much about testing. Here is why:

  • When you talk about tests, you mostly think you need to validate how the code does something. That’s not what you should do. In fact you should not care at all how the code does someting, you should only care about what it does, In short, you want to know it the codes has a desired behaviour. So lets replace the word “test” with another catchy name spec. So from now on you are not writing tests to test something, but you are writing specifications for behaviours. Sweet.

  • Everybody has a different idea what a unit is. Some think it’s a class, others think it is a tiny piece of code, others talk about an entity of code that somehow belongs together. This ambiguousness is bad, so let’s ditch it. Lets just talk about behaviours: This is independent of the structure of what you want to test, and clearly describes what you should be validating all along; if you talk about unit tests you are limiting your scope to whatever you think a unit represents. When thinking about behaviours you are free to validate what you really should.

  • The syntax of the asserts can be cleaned up quite a bit. So in Ruby with rUnit you write assert_equals(expected, actual), but wouldn’t it be much nicer if you could write actual.should_be expected. In fact this is exactly how it works in rSpec.

What now?

Behaviour Driven Development is a very recent invention, and work around this has just started. I expect that after rSpec we will soon see jSpec, pSpec, and lots of other tools. I hope this will change peoples mindset and allows us to grok how software engineering should work more thoroughly.

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