die.rb

class Die 
  def initialize(number_of_sides)
    @number_of_sides = number_of_sides
  end

  def sides
    @number_of_sides
  end

  def roll 
    rand(@number_of_sides - 1) + 1
  end 

end 

die_program.rb

require './lib/die'

def main_menu
  puts "Press 'c' to create a new die, 'r' to roll your die or 'e' to exit"
  main_choice = gets.chomp
  if main_choice == 'c'
    create_die
  elsif main_choice == 'r'
    roll_die
  elsif main_choice == 'e'
    puts "Good-bye!"
  else
    puts "Sorry, that wasn't a valid option."
    main_menu
  end
end

def create_die
  puts "How many sides do you want in your die?"
  @sides = gets.to_i
  @die = Die.new(@sides)
  puts "\n"
  puts "You created a die with #{@die.sides} sides."
  main_menu
end

def roll_die
  if @die.nil?
    puts "You have not created a die yet. Please create a die before rolling"
  else
    puts "You rolled a #{@die.roll}."
  end

  main_menu
end

main_menu  

die_spec.rb

require 'rspec'
require 'die'

describe Die do
  it 'initialized with specified number of sides' do
    die = Die.new(6)
    die.should be_an_instance_of Die
  end

  it 'lets you read the number of sides out' do 
    test_die = Die.new(12)
    test_die.sides.should eq 12
  end

  it 'rolls the die with a random number (1 to the number of sides)' do
    test_die = Die.new(12)
    test_die.stub(:rand) {11}
    test_die.roll.should eq 12
  end  
end