rps.rb

require 'test/unit'

class Piece
  def self.beats(type)
    self.instance_eval do
      define_method "beats_#{type}?".intern do
        true
      end
    end
  end
  
  def method_missing(type)
    false
  end
  
end

class Rock < Piece
  beats :scissors
end

class Paper < Piece
  beats :rock
end

class Scissors < Piece
  beats :paper  
end

# TEST METHODS
class RPS_Test < Test::Unit::TestCase
  
  def setup
    @rock = Rock.new()
    @scissors = Scissors.new()
    @paper = Paper.new()
  end
  
  def test_rock_should_beat_scissors
    assert(@rock.beats_scissors?, "Rock should beat scissors.")
  end
  
  def test_scissors_should_beat_paper
    assert(@scissors.beats_paper?, "Scissors should beat paper.")
  end
  
  def test_paper_should_beat_rock
    assert(@paper.beats_rock?, "Paper should beat rock.")
  end
  
  def test_scissors_should_lose_to_rock
    assert(!@scissors.beats_rock?, "Scissors cannot beat rock.")
  end
  
  def test_rock_should_lose_to_paper
    assert(!@rock.beats_paper?, "Rock cannot beat paper.")
  end
  
  def test_paper_should_lose_to_scissors
    assert(!@paper.beats_scissors?, "Paper cannot beat scissors.")
  end
    
end