blog_post.rb

class BlogPost
  def initialize(text)
    @text = text
  end

  def word_list
    @text.scan(/[a-zA-Z0-9_@-]+/)
  end
end

blog_post_test.rb

require 'rubygems'
require 'test/unit'
require 'shoulda'

require 'blog_post'

class BlogTest < Test::Unit::TestCase

  context "A Blog Post" do
    setup { @text = "Some words"}
    should("exist") { assert_not_nil post }

    context "with a simple word list" do
      should("report its word list") do
        assert_equal ['Some', 'words'], post.word_list
      end
    end

    context "with a complex word list" do
      setup { @text =
        "A word list, with: Punctuation. " +
        "Why; not? because* [it] (should)."
      }
      should("report its word list") do
        assert_equal(
          %w(A word list with Punctuation Why not because it should),
          post.word_list)
      end
    end

    context "with a unusual words" do
      setup { @text = "a-long_word99" }
      should("report its word list") do
        assert_equal ['a-long_word99'], post.word_list
      end
    end
  end

  private

  def post
    @post ||= BlogPost.new(@text)
  end
end

does_my_blog_post_suck.rb

require 'twitter_trending_words'

class DoesMyBlogPostSuck
  def initialize(post)
    @post = post
  end

  def does_this_blog_post_suck?
    word_count < 10 ||
      word_count > 100 ||
      objectionable_word_count >= 3 ||
      twitter_word_count == 0
  end

  private

  OBJECTIONABLE_WORDS = ['um', 'like', 'really']

  def word_list
    @word_list ||= @post.word_list
  end

  def word_count
    @word_count ||= word_list.size
  end

  def objectionable_word_count
    word_list.inject(0) { |c, w| OBJECTIONABLE_WORDS.include?(w) ? c+1 : c }
  end

  def twitter_word_count
    TwitterTrendingWords.list.inject(0) { |c, word|
      word_list.include?(word) ? c+1 : c
    }
  end
end

does_my_blog_post_suck_test.rb

require 'rubygems'
require 'test/unit'
require 'shoulda'
require 'flexmock/test_unit'

require 'does_my_blog_post_suck'
require 'blog_post'
require 'twitter_trending_words'

class BlogTest < Test::Unit::TestCase
  context "A DoesMyBlogPostSuck object" do
    setup { flexmock(TwitterTrendingWords).should_receive(:list => ['Ruby', 'Python', 'Clojure']) }
    setup { @text =
      "This is a blog post that should be ok. " +
      "Other than that, it is pretty boring. " +
      "Oh, and it should mention the Ruby language."
    }

    context "with no objectionable words" do
      should("be ok") { assert_ok }
    end

    context "with two objectionable words" do
      setup { @text << "this is um ok, really." }
      should("be ok") { assert_ok }
    end

    context "with three objectionable words" do
      setup { @text << "this is um like ok, really." }
      should("suck") { assert_sucks }
    end

    context "with fewer than ten words" do
      setup { @text = words(9) }
      should("suck") { assert_sucks }
    end

    context "with ten words" do
      setup { @text = words(10) }
      should("be ok") { assert_ok }
    end

    context "with 100 words" do
      setup { @text = words(100) }
      should("be ok") { assert_ok }
    end

    context "with 101 words" do
      setup { @text = words(101) }
      should("be too long, so it sucks") { assert_sucks }
    end

    context "without twitter trending words" do
      setup { @text.gsub!(/ruby/i, '') }
      should("be irrelevant, so it sucks") { assert_sucks }
    end

    context "with several defects" do
      setup { @text = "um like really" }
      should("still suck") { assert_sucks }
    end
  end

  private

  def suck_detector
    post = BlogPost.new(@text)
    @suck_detector ||= DoesMyBlogPostSuck.new(post)
  end

  def words(n)
    (["Ruby"] * n).join(" ")
  end

  def assert_ok
    assert ! suck_detector.does_this_blog_post_suck?
  end

  def assert_sucks
    assert suck_detector.does_this_blog_post_suck?
  end
end

Rakefile

#!/usr/bin/env ruby"

require 'rake/clean'
require 'rake/testtask'

task :default => :test

Rake::TestTask.new(:test) do |t|
  t.warning = true
  t.verbose = false
  t.test_files = FileList['*_test.rb']
end

twitter_trending_words.rb

class TwitterTrendingWords
  def self.list
    fail "Not Implemented"
  end
end