describe BlogPost do
  before do
    @blog_post = BlogPost.create :title => 'Hello'
  end

  it "does something" do
    @blog_post.should ...
  end

  it "does something else" do
    @blog_post.should ...
  end
end

However, recently I stumbled upon a cleaner approach in a presentation (from which I borrowed the examples in this article) by Jon Larkowski that makes use of RSpec’s let() method. With this approach, the example from above looks like:

describe BlogPost do
  let(:blog_post) { BlogPost.create :title => 'Hello' }

  it "does something" do
    blog_post.should ...
  end

  it "does something else" do
    blog_post.should ...
  end
end

At first this looked quite magic to me and I had no clue how it worked. Though a look at the source of the let() method reveals the magic (the code should be self-explanatory, or else please leave a comment):

def let(name, &block)
  define_method name do
    @assignments ||= {}
    @assignments[name] ||= instance_eval(&block)
  end
end

Happy RSpecing!

What I like about BDD is the simple, but powerful concept of Given-When-Then for specifying scenarios. It is a concept you can also use without doing BDD to specify the requirements of your application.

It simply defines the structure of how you write down the requirements in the form of scenarios (as a sidenote: in BDD, a scenario belongs to a feature. For example, a “Login” feature might consist of the scenarios “Login with username/password” and “Login with OpenID”):

Given some initial context (the givens),
When an event occurs,
Then ensure some outcomes.

(from http://dannorth.net/introducing-bdd)

“Given” defines the preconditions, “When” defines what happens, and “Then” defines the result of the scenario. Or in other words: “Given” describes the start state, and “When” the steps necessary to reach the accepting state (= “Then”).

A simple example of a “Publish new article” scenario might look like:

Given I am logged in
When I write an article with the title "My article"
And I publish the article
Then I should see the message "Article published"
And the article "My article" should appear on the homepage

The simplicity of this format makes it easy to discuss the requirements of your application. And thanks to tools like Cucumber you can even make such specifications executable, but that’s something for another post…