Test Ruby code in Markdown files.

doctest.rb

#!/usr/bin/env ruby

pattern = /^```(.*)/
capturing = false
language = ''
lines = {}

File.open(ARGV.shift).each_line do |line|
  match = pattern.match(line)

  if match
    unless capturing
      language = match[1].downcase.strip
      lines[language] ||= []
    end

    capturing = !capturing
  else
    lines[language] << line if capturing
  end
end

pattern = /^#( =>)? (.*)/
buffer = []

lines.fetch('ruby').each do |line|
  match = pattern.match(line)

  if match
    code = buffer.join
    expected = match[2]

    if match[1]
      actual = eval(code).inspect
    else
      begin
        eval(code)
      rescue => error
        actual = "#{error.class}: #{error.message}"
      end
    end

    unless actual == expected
      puts 'FAILURE'
      puts "Expected: #{expected}"
      puts "Actual: #{actual}"
      puts "Code: #{code}"
      puts
    end

    buffer = []
  else
    buffer << line
  end
end