Bowling kata

bowling.rb

class Game
  attr_reader :rolls

  def initialize(rolls)
    @rolls = rolls
  end

  def score
    frames.inject(0) do |score, frame|
      score += FrameScorer.new(frame).score
    end
  end

  def frames
    Enumerator.new do |yielder|
      position = 0

      10.times do
        yielder << rolls[position,3].map(&:to_i)

        if rolls[position] == 10
          position += 1
        else
          position += 2
        end
      end
    end
  end
end

class FrameScorer
  attr_reader :rolls

  def initialize(rolls)
    @rolls = rolls
  end

  def score
    if spare? or strike?
      sum_all_rolls
    else
      sum_first_two_rolls
    end
  end

  def strike?
    rolls[0] == 10
  end

  def spare?
    sum_first_two_rolls == 10
  end

  def sum_first_two_rolls
    rolls[0,2].inject(&:+)
  end

  def sum_all_rolls
    rolls.inject(&:+)
  end
end

bowling_spec.rb

require_relative "../bowling"

describe Game do
  subject { Game.new(@rolls) }

  it "scores a frame" do
    @rolls = [4,5,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0]
    subject.score.should eq(9)
  end

  it "scores two frames" do
    @rolls = [4,5,4,5,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0]
    subject.score.should eq(18)
  end

  it "scores two frames with spares" do
    @rolls = [5,5,5,5,5,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0]
    subject.score.should eq(35)
  end

  it "scores two frames with strikes" do
    @rolls = [10,10,5,4,0,0,0,0,0,0,0,0,0,0,0,0,0,0]
    subject.score.should eq(53)
  end

  it "scores a perfect game" do
    @rolls = [10,10,10,10,10,10,10,10,10,10,10,10]
    subject.score.should eq(300)
  end
end

describe FrameScorer do
  subject { FrameScorer.new(@rolls) }

  it "can score two zeros" do
    @rolls = [0,0]
    subject.score.should eq(0)
  end

  it "can score < 10" do
    @rolls = [4,5]
    subject.score.should eq(9)
  end

  it "can score a spare" do
    @rolls = [4,6,5]
    subject.score.should eq(15)
  end

  it "does not overscore" do
    @rolls = [4,5,8]
    subject.score.should eq(9)
  end

  it "can score a strike" do
    @rolls = [10,5,4]
    subject.score.should eq(19)
  end
end