Rails - Oct 2007 - Scenarios, an Alternative to Fixtures

Being fully aware of the work of Mr. Preston-Werner[1] and
err.the.blog[2], we present to you Scenarios, a somewhat different
approach[3] to alleviating the pain of managing table data for a Rails
application under test.

A simple scenario looks like this:

  # in spec/scenarios/users_scenario.rb
  class UsersScenario < Scenario::Base
    def load
      create_record :user, :john, :name => ''John'',
:password =>
''doodaht''
      create_record :user, :cindy, :name => ''Cindy'',
:password =>
''whoot!''
    end
  end

To use the UsersScenario in an RSpec description, you should declare
it using
the scenario method:

  # in spec/models/user_spec.rb
  describe User do
    scenario :users

    it "should allow me to do something with John" do
      user = users(:john)
      user.password.should == "doodaht"
    end
  end

In real life your scenarios will probably grow quite complicated. The
scenarios plugin allows you to deal with this complexity through
composition.

Here''s a simple example:

  # in spec/scenarios/posts_scenario.rb
  class PostsScenario < Scenario::Base
    def load
      create_record :post, :first, :title => "First Post"
      create_record :post, :second, :title => "Second Post"
    end
  end

  # in spec/scnearios/comments_scenario.rb
  class CommentsScenario < Scenario::Base
    uses :posts

    def load
      create_record :comment, :first, :body => "Nice post!",
:post_id
=> post_id(:first)
      create_record :comment, :second, :body => "I like it.",
:post_id
=> post_id(:first)
      create_record :comment, :third, :body => "I thoroughly
disagree.", :post_id => post_id(:second)
    end
  end

When you use a scenario, you get any help the scenario provides made
available to your RSpec examples.

  # in spec/scenarios/users_scenario.rb
  class UsersScenario < Scenario::Base
    def load
      create_user :name => "John"
    end

    helpers do
      def create_user(attributes={})
        create_record :user, attributes[:name].downcase.intern,
attributes
      end
      def login_as(user)
        @request.session[:user_id] = user.id
      end
    end
  end

  # in spec/controllers/projects_controller_spec.rb
  describe "Projects screen" do
    scenario :users

    it "should show active projects" do
      login_as(users(:john))
      get :projects
      @response.should have_tag(''#active_projects'')
    end
  end

You can load your scenarios into your development database, too!

   rake db:scenario:load SCENARIO=comments


Scenarios works by doing direct inserts instead of using ActiveRecord
instances - there is no validation - similar to the way the current
fixtures implementation works.

You may find greater detail at the RubyForge project site[4]. Any
feedback from those seeing value and giving it a spin is greatly
appreciated.

   Adam Williams



1. http://code.google.com/p/fixture-scenarios/
2. http://errtheblog.com/post/7708
3. http://rubyforge.org/pipermail/rspec-users/2007-October/003883.html
4. http://faithfulcode.rubyforge.org/svn/plugins/trunk/scenarios/README


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