check_required_ivars

# File actionpack/lib/action_controller/test_case.rb, line 621
      def check_required_ivars
        # Sanity check for required instance variables so we can give an
        # understandable error message.
        [:@routes, :@controller, :@request, :@response].each do |iv_name|
          if !instance_variable_defined?(iv_name) || instance_variable_get(iv_name).nil?
            raise "#{iv_name} is nil: make sure you set it in your test's setup method."
          end
        end
      end