Roman numbers calculator (did as kata with Ruby and RSpec).

roman_numbers.rb

require "rspec"

CONVERSIONS_FACTOR = [
    [100, "C"], [90, "XC"], [50, "L"], [40, "XL"], [10, "X"], [9, "IX"], [5, "V"], [4, "IV"], [1, "I"]
]
def conversion_factors_for number
  CONVERSIONS_FACTOR.find { |arabic, _| arabic <= number }
end

def convert number
  return "" if number.zero?
  arabic, roman = conversion_factors_for number
  roman + convert(number - arabic)
end

describe "Converting arabic numbers to roman numbers" do
  context "Romans didn't have a 0" do
    it "converts 0 to a blank string" do
      expect(convert(0)).to eq("")
    end
  end

  {
      1 => "I",
      2 => "II",
      4 => "IV",
      5 => "V",
      6 => "VI",
      10 => "X",
      16 => "XVI",
      20 => "XX",
      40 => "XL",
      50 => "L",
      100 => "C",
      90 => "XC"

  }.each_pair do |arabic, roman|
    it "converts #{arabic} to #{roman}" do
      expect(convert(arabic)).to eq(roman)
    end
  end
end