assign_parameters

# File actionpack/lib/action_controller/test_case.rb, line 73
    def assign_parameters(routes, controller_path, action, parameters, generated_path, query_string_keys)
      non_path_parameters = {}
      path_parameters = {}

      parameters.each do |key, value|
        if query_string_keys.include?(key)
          non_path_parameters[key] = value
        else
          if value.is_a?(Array)
            value = value.map(&:to_param)
          else
            value = value.to_param
          end

          path_parameters[key] = value
        end
      end

      if get?
        if query_string.blank?
          self.query_string = non_path_parameters.to_query
        end
      else
        if ENCODER.should_multipart?(non_path_parameters)
          self.content_type = ENCODER.content_type
          data = ENCODER.build_multipart non_path_parameters
        else
          fetch_header("CONTENT_TYPE") do |k|
            set_header k, "application/x-www-form-urlencoded"
          end

          case content_mime_type.to_sym
          when nil
            raise "Unknown Content-Type: #{content_type}"
          when :json
            data = ActiveSupport::JSON.encode(non_path_parameters)
          when :xml
            data = non_path_parameters.to_xml
          when :url_encoded_form
            data = non_path_parameters.to_query
          else
            @custom_param_parsers[content_mime_type.symbol] = ->(_) { non_path_parameters }
            data = non_path_parameters.to_query
          end
        end

        data_stream = StringIO.new(data)
        set_header "CONTENT_LENGTH", data_stream.length.to_s
        set_header "rack.input", data_stream
      end

      fetch_header("PATH_INFO") do |k|
        set_header k, generated_path
      end
      path_parameters[:controller] = controller_path
      path_parameters[:action] = action

      self.path_parameters = path_parameters
    end