changes.rb

class Changes < Actor
  out :timeline_tweets_out
  takes :tweets_in, :friends_in

  def before
    @friends = @friends_in.pop
  end

  def pump
    tweet = @tweets_in.pop
    timeline_tweets_out << tweet if @friends.include_user?(tweet.user)
  end
end

changes_spec.rb

describe Changes do
  let(:tweets_queue) { SelectableQueue.new }
  let(:gary) { User.new(1, "garybernhardt") }
  let(:corey) { User.new(2, "coreyhaines") }
  let(:friends) { Friends.new([gary]) }
  let(:friends_queue) { SelectableQueue.with_objects([friends]) }
  let(:changes) { Changes.new(tweets_queue, friends_queue) }

  before do
    tweets_queue << tweet
    changes.before
    changes.pump
  end

  context "when we follow the tweeter" do
    let(:tweet) { Tweet.new(1, gary, "#lolruby") }

    it "is added to the timeline queue" do
      changes.timeline_tweets_out.pop.should == tweet
    end
  end

  describe "when we have no relationship to the tweeter" do
    let(:tweet) { Tweet.new(1, corey, "#lolruby") }

    it "isn't added to any queues" do
      changes.timeline_tweets_out.empty?.should == true
    end
  end
end