generative.rb

# Subject under test
def to_arabic(roman)
  roman.chars.each_with_index.map { |x, i|
    next_x = roman[i + 1]
    if x == "I"
      ["V", "X"].include?(next_x) ? -1 : 1
    elsif x == "V"
      next_x == "X" ? -5 : 5
    elsif x == "X"
      next_x == "C" ? -10 : 10
    end
  }.reduce(:+)
end

# Test
class Generative < SmellTest
  EXAMPLES = {
    "I" => 1,
    "II" => 2,
    "III" => 3,
    "IV" => 4,
    "V" => 5,
    "VI" => 6,
    "VII" => 7,
    "VIII" => 8,
    "IX" => 9,
    "X" => 10
  }.each do |(roman, arabic)|
    define_method "test_roman_#{roman}_is_#{arabic}" do
      result = to_arabic(roman)

      assert_equal result, arabic
    end
  end
end