normalize_argument_to_redirection

# File actionpack/lib/action_dispatch/testing/assertions/response.rb, line 77
        def normalize_argument_to_redirection(fragment)
          case fragment
          when %{^\w[A-Za-z\d+.-]*:.*}
            fragment
          when String
            @request.protocol + @request.host_with_port + fragment
          when :back
            raise RedirectBackError unless refer = @request.headers["Referer"]
            refer
          else
            @controller.url_for(fragment)
          end.gsub(/[\r\n]/, '')
        end