detect_double_xss_protection.rb

Before do
  Capybara.current_session.driver.rack_mock_session.after_request do
    body = Capybara.current_session.driver.response.body

    if match = body.match(%r{<\w+(?:\s+\w+\s*=\s*"[^&]+")*\s*/?>})
      puts "WARNING: escaped tag: " +
        match[0].gsub("&lt;", "<").gsub("&gt;", ">").gsub("&quot;", '"')
    end

    if match = body.match(%r{&amp;(\w+);})
      puts "WARNING: escaped entity: &#{match[1]};"
    end
  end
end

thanks @jferris I'll look into that next time I have some spare time! ;)