CC validation refactoring exercise

README.md

You need RSpec installed to run these tests.

gem install rspec
rspec credit_card_spec.rb

The CreditCard class is currently working but the code is in need of some refactoring. Refactor it (ensuring that the specs continue to pass) and when you are finished, share the gist with us.

Feel free to include in your gist a README containing an explanation of your refactorings and any thoughts or philosophies behind what you did. We're particularly interested in understanding what you personally consider to be good code, and this exercise will help us see into that a bit.

credit_card.rb

class CreditCard
  
  def initialize(ccn)
    @ccn = ccn.to_s.split("").each { |string| string.to_i}
    @ccn_ints = @ccn.map(&:to_i)
    raise ArgumentError, "Invalid credit card number" if @ccn.size != 16 
  end
  
  def valid?
    change_numbers = []
    product_sum = []
    counter = 1
    @ccn_ints.each do |x|
      if counter % 2 == 0
        change_numbers << (x * 2)
      else
        change_numbers << x
      end
      
      counter += 1
    end
    
    change_numbers.each do |element|
      if element < 10
        product_sum << element
      else
        product_sum << (element / 10)
        product_sum << (element % 10)
      end
    end
    
    sum = 0
    product_sum.each { |a| sum += a }
    sum % 10 == 0
  end
end

credit_card_spec.rb

require 'rspec'
require_relative 'credit_card'

describe CreditCard do
  describe '#initialize' do
    it 'Expects a single argument for the card' do
      CreditCard.instance_method(:initialize).arity.should eq 1
    end
    
    it 'raises ArgumentError on card > 16' do
      expect {
        CreditCard.new(11111111111111112)
      }.to raise_error(ArgumentError)
    end
    
    it 'raises ArgumentError on card < 16' do
      expect {
        CreditCard.new(1)
      }.to raise_error(ArgumentError)
    end
  end
  
  describe '#valid?' do
    it 'expects no arguments to be passed' do
      CreditCard.instance_method(:valid?).arity.should be_zero
    end
    
    it 'returns true for a valid card' do
      card = CreditCard.new(4408041234567893)
      
      card.should be_valid
    end
    
    it 'returns false for a bad card' do
      card = CreditCard.new(4408041234567892)
      
      card.should_not be_valid
    end
  end
end