cards.rb

class Card
  ROYALS = [:jack, :queen, :king, :ace]

  def initialize(value)
    @value = if value.class == Symbol then
               raise RuntimeError unless ROYALS.index(value) >= 0
               ROYALS.index(value) + 11 
             else
               val = value.to_i
               raise RuntimeError unless val > 1 && val < 15
               val
             end
  end

  def to_i
    @value
  end

  def > (card)
    to_i > card.to_i
  end
  def < (card)
    to_i < card.to_i
  end
  def == (card)
    to_i == card.to_i
  end
end

class Deck
  def initialize
    @cards = []
    52.times do
      @cards << Card.new(2+rand(13))
    end
  end

  def size
    @cards.length
  end

  def deal(amount=1)
    @cards.pop
  end

  def peek
    @cards.last
  end

  def shuffle
    @cards.pop
    self
  end
end

cardtests.rb

require 'test/unit'
require 'cards'

class CardTest < Test::Unit::TestCase
  def setup
  end

  def test_a_five_is_greater_than_a_two
    five_card = Card.new(5)
    two_card = Card.new(2) 
    assert five_card > two_card
  end

  def test_a_ten_is_less_than_a_king
    ten_card = Card.new(10)
    king_card = Card.new(:king)
    assert ten_card < king_card
  end

  def test_two_twos_are_equal
    two_card = Card.new(2)
    two_card2 = Card.new(2)
    assert two_card == two_card2
  end

  def test_setting_rank_with_string_vs_integer_doesnt_matter
    two_card = Card.new(2)
    two_card2 = Card.new("2")
    assert two_card == two_card2
  end

  def test_card_constructor_rejects_invalid_arguments
    assert_raise RuntimeError do
      bad_card = Card.new("SF")
    end
    assert_raise RuntimeError do
      bad_card = Card.new(1)
    end
    assert_raise RuntimeError do
      bad_card = Card.new(22)
    end
  end

  def teardown
  end
end

class DeckTest < Test::Unit::TestCase
  def setup
  end

  def test_size_of_new_deck_is_52
    deck = Deck.new
    assert deck.size == 52
  end

  def test_dealing_one_reduces_size_of_deck_by_one
    deck = Deck.new
    deck.deal
    assert deck.size == 51
  end

  def test_dealing_five_reduces_size_of_deck_by_five
    deck = Deck.new
    5.times { deck.deal }
    assert deck.size == 47
  end

  def test_peek_shows_next_card_without_dealing_it
    deck = Deck.new
    assert deck.peek == deck.deal
  end    

  def test_shuffling_changes_order_of_deck
    deck = Deck.new
  end

  def test_shuffling_preserves_all_the_original_cards
  end

  def teardown
  end
end