The result of my 2nd attempt at the Roman Numerals Kata

roman_numerals.rb

class Fixnum

  ROMAN_CONVERSION = [
    [1000, 'M' ],
    [900,  'CM'],
    [500,  'D' ],
    [400,  'CD'],
    [100,  'C' ],
    [90,   'XC'],
    [50,   'L' ],
    [40,   'XL'],
    [10,   'X' ],
    [9,    'IX'],
    [5,    'V' ],
    [4,    'IV'],
    [1,    'I' ]
  ]

  def to_roman
    num    = self
    result = ""

    ROMAN_CONVERSION.each do |arabic, roman|
      div, num = num.divmod(arabic)

      result << roman * div
    end

    result
  end

  def self.from_roman(numeral)
    num_str = numeral.dup
    result  = 0

    ROMAN_CONVERSION.each do |arabic, roman|
      while num_str.start_with?(roman)
        num_str.slice!(roman)
        result += arabic
      end
    end

    result
  end

end

roman_numerals_spec.rb

require_relative File.join("..", "lib", "roman_numerals")

  TEST_CASES = [
    [1,    'I'],
    [2,    'II'],
    [3,    'III'],
    [4,    'IV'],
    [5,    'V'],
    [6,    'VI'],
    [7,    'VII'],
    [8,    'VIII'],
    [9,    'IX'],
    [10,   'X'],
    [14,   'XIV'],
    [16,   'XVI'],
    [19,   'XIX'],
    [23,   'XXIII'],
    [42,   'XLII'],
    [50,   'L'],
    [80,   'LXXX'],
    [99,   'XCIX'],
    [128,  'CXXVIII'],
    [438,  'CDXXXVIII'],
    [500,  'D'],
    [999,  'CMXCIX'],
    [1776, 'MDCCLXXVI'],
    [1985, 'MCMLXXXV']
  ]

describe Fixnum, "#to_roman" do
  TEST_CASES.each do |arabic, roman|
    it "should convert #{arabic} to #{roman}" do
      arabic.to_roman.should == roman
    end
  end
end

describe Fixnum, "#from_roman" do
  TEST_CASES.each do |arabic, roman|
    it "should convert #{roman} to #{arabic}" do
      Fixnum.from_roman(roman).should == arabic
    end
  end
end