luhn_algorithm.rb

require 'minitest/autorun'

module Luhn
  def self.is_valid?(number)
	digits = number.to_s.split("")
	digits.map! {|x| x.to_i }
 	ary = Array.new
 		
 	digits.each_with_index do |value, index|
	  if index.even?
		ary << value * 2
	  else
		ary << value
	  end
 	end

	ary.map! {|x| (x >= 10 ? x-9 : x)}
	sum = ary.inject(:+)

	if sum % 10 == 0
	  return true
	else
	  return false
	  end
  end
end

class TestLuhn < MiniTest::Unit::TestCase

  def test_luhn_valid
	assert Luhn.is_valid?(4194560385008504)
  end

  def test_luhn_invalid
	assert ! Luhn.is_valid?(4194560385008505)
  end

end