Luhn Algorithm - validate credit card numbers

luhn.rb

require 'minitest/autorun'

module Luhn
  # number must be a string
  # number = number.to_s

  def self.is_valid?(number)
    array = number.to_s.split('')
    array = array.reverse
    array = array.map.with_index do |x, i|
    x = x.to_i
    # for the last item in the list, i = 0
      if i % 2 == 1
        x = x * 2
        if x >= 10
          x = x - 9
        end
      end
      x
    end
    array = array.inject(:+)
    if array % 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