# File lib/fog/aws/requests/efs/describe_file_systems.rb, line 35
        def describe_file_systems(options={})
          response = Excon::Response.new

          file_systems = if id = options[:id]
                           if fs = self.data[:file_systems][id]
                             [fs]
                           else
                             raise Fog::AWS::EFS::NotFound.new("invalid file system ID: #{id}")
                           end
                         elsif creation_token = options[:creation_token]
                           fs = self.data[:file_systems].values.detect { |file_system| file_system["CreationToken"] == creation_token }
                           [fs]
                         else
                           self.data[:file_systems].values
                         end

          file_systems.each do |file_system|
            file_system['LifeCycleState'] = 'available'
            self.data[:file_systems][file_system['FileSystemId']] = file_system
          end

          response.body = {"FileSystems" => file_systems}
          response
        end