Ruby Quiz Solution

roman.rb

def roman_to_arabic
  {'M' => 1000, 'CM' => 900, 'D' => 500, 'CD' => 400, 
   'C' => 100,  'XC' => 90,  'L' => 50,  'XL' => 40, 
   'X' => 10,   'IX' => 9,   'V' => 5,   'IV' => 4, 
   'I' => 1}
end

def to_roman n
  roman_to_arabic.map do |roman, arabic|
    i, n = n.divmod(arabic)
    roman * i 
  end.join
end

def from_roman n
  roman_to_arabic.values_at(
    *n.scan(/CM|CD|XC|XL|IX|IV|./)
  ).reduce(:+)
end

def convert n
  n =~ /\d/ ? to_roman(n.to_i) : from_roman(n)
end

ARGF.each_line {|l| puts convert(l)}  if $0 == __FILE__

roman_test.rb

require 'test/unit'
require './roman'

class RomanTest < Test::Unit::TestCase
  def test_I_is_1
    assert(from_roman("I") == 1)
  end

  def test_IV_is_4
    assert(from_roman("IV") == 4)
  end

  def test_VIII_is_8
    assert(from_roman("VIII") == 8)
  end

  def test_CCXCI_is_291
    assert(from_roman("CCXCI") == 291)
  end

  def test_MCMXCIX_is_1999
    assert(from_roman("MCMXCIX") == 1999)
  end

  def test_XXXVIII_is_38
    assert(from_roman("XXXVIII") == 38)
  end

  def test_XXIX_is_29
    assert(from_roman("XXIX") == 29)
  end

  def test_1_is_I
    assert(to_roman(1) == "I")
  end

  def test_2_is_II
    assert(to_roman(2) == "II")
  end

  def test_4_is_IV
    assert(to_roman(4) == "IV")
  end

  def test_45_is_XLV
    assert(to_roman(45) == "XLV")
  end

  def test_291_is_CCXCI
    assert(to_roman(291) == "CCXCI")
  end

  def test_1999_is_MCMXCIX
    assert(to_roman(1999) == "MCMXCIX")
  end

  def test_38_is_XXXVIII
    assert(to_roman(38) == "XXXVIII")
  end
end