Shuffler.rb

class Shuffler
  attr_reader :list

  def initialize(list)
    @list = list
  end

  def shuffle
    i = @list.length - 1
    while i >= 0
      x = rand(i)

      @list[i], @list[x] = @list[x], @list[i]

      i = i - 1
    end
  end
end

Shuffler_spec.rb

require './Shuffler.rb'

deck = []
for suit in ['S', 'H', 'D', 'C']
  for card in ['1', '2', '3', '4', '5', '6', '7', '8', '9', 'J', 'Q', 'K', 'A']
    deck.push "#{suit}#{card}"
  end
end

describe Shuffler, '#shuffle' do
  it 'returns a randomized deck of cards' do
    shuffler = Shuffler.new deck.dup
    shuffler.shuffle()
    shuffler.list.should_not == deck
  end
end