from_roman_test.rb

require 'minitest/autorun'

ARABIC_VALUES = {
  'I' => 1, 'V' => 5, 'X' => 10, 'L' => 50, 'C' => 100, 'D' => 500, 'M' => 1000
}

def from_roman(roman)
  chars = roman.chars << 'I'
  chars.each_cons(2).inject(0) do |sum, (c1, c2)|
    sum + (ARABIC_VALUES[c1] < ARABIC_VALUES[c2] ? -ARABIC_VALUES[c1] : ARABIC_VALUES[c1])
  end
end

class RomanConversions < Minitest::Test
  def test_from_roman
    assert_equal 1, from_roman('I')
    assert_equal 2, from_roman('II')
    assert_equal 3, from_roman('III')
    assert_equal 5, from_roman('V')
    assert_equal 6, from_roman('VI')
    assert_equal 8, from_roman('VIII')
    assert_equal 10, from_roman('X')
    assert_equal 30, from_roman('XXX')
    assert_equal 24, from_roman('XXIV')
    assert_equal 42, from_roman('XLII')
    assert_equal 2014, from_roman('MMXIV')
    assert_equal 1999, from_roman('MCMXCIX')
    assert_equal 666, from_roman('DCLXVI')
    assert_equal 444, from_roman('CDXLIV')

    assert_equal 4, from_roman('IV')
    assert_equal 9, from_roman('IX')
  end
end