Two flavours of BDD, or .net gets behaviour-driven

How about that? You wait ages for a BDD framework in .net and then two come along at once! Ok, to be fair NSpec has been around for a while. However I’m talking about describing application behaviour in terms of stories and scenarios, to complement NSpec’s description of interactions between objects. (As a side note, I would love to see NSpec adopt rspec’s describe/it vocabulary rather than using contexts and specifications.)

Introducing NBehave and, well, NBehave! ¶

Morgan Persson first spoke to me about writing a .net version of JBehave at the beginning of 2007¹, so I am delighted that he has just announced his first public release of NBehave. It mixes C# and VB.net in a lovely it’s-all-about-the-CLR way. So the examples are in C#, extending VB.net framework classes.

In the meantime, Joe Ocampo has used some C#3 voodoo to create something scarily similar to rbehave for .net. He seemed to produce this in slightly less time than it took me to press “publish” in WordPress, and I have to say it looks great.

Two use cases for expressing intent ¶

The original idea behind the JBehave story framework was that developers would write “pluggable” givens, events and outcomes to define the various scenarios that make up each story. Non-technical people would then manipulate these using desktop tools (say a graphical story builder where you drag the various components around to define your stories and scenarios).

rbehave has a different motivation, namely moving from the textual representation of a story to an executable definition in as few steps as possible. This is to allow human beings—mainly testers and business analysts—to read, write and edit executable acceptance criteria.

Liz Keogh and I are currently preparing a JBehave tutorial for OOPSLA 2007. Since JBehave was based very much on the first use case, we’ve noticed it is pretty painful to pull together a story from a standing start, without a proliferation of tiny classes emerging. I’m working on a fluent interface that is currently looking a little like this:

public Story story() {
  return newStory("I can create a cell").
    asA("game producer").
    iWant("to create a cell").
    soThat("I can show the grid to people").
    withScenarios(
      scenario("Nothing to see here",
        given("a game with dimensions", 3, 3),
        then("the grid should look like",
            "...",
            "...",
            "...")
    )
  );
}

It’s backed by the regular JBehave classes and runs in the standard JBehave story runner.

I would love to see Morgan and Joe bring their two interpretations of acceptance-level BDD together into a single framework. It is after all just a bunch of scenario fragments playing nice together, and having the two approaches to expressing intent in the same framework means that NBehave could be both a directly-editable representation of behaviour, and at the same time the basis of a (graphical?) toolset for defining acceptance criteria in .net. Maybe even as a Visual Studio plugin.