    # File lib/action_controller/test_process.rb, line 374
        def process(action, parameters = nil, session = nil, flash = nil)
          # Sanity check for required instance variables so we can give an
          # understandable error message.
          %w(@controller @request @response).each do |iv_name|
            if !(instance_variable_names.include?(iv_name) || instance_variable_names.include?(iv_name.to_sym)) || instance_variable_get(iv_name).nil?
              raise "#{iv_name} is nil: make sure you set it in your test's setup method."
            end
          end

          @request.recycle!

          @html_document = nil
          @request.env['REQUEST_METHOD'] ||= "GET"
          @request.action = action.to_s

          parameters ||= {}
          @request.assign_parameters(@controller.class.controller_path, action.to_s, parameters)

          @request.session = ActionController::TestSession.new(session) unless session.nil?
          @request.session["flash"] = ActionController::Flash::FlashHash.new.update(flash) if flash
          build_request_uri(action, parameters)
          @controller.process(@request, @response)
        end