You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: group.rb
    path of file: ./repos/fastlane/spaceship/lib/spaceship/test_flight
    
    the code of the file until where you have to start completion: require_relative 'base'
require_relative 'build'

module Spaceship::TestFlight
  class Group < Base
    attr_accessor :id
    attr_accessor :name
    attr_accessor :is_default_external_group
    attr_accessor :is_internal_group
    attr_accessor :provider_id
    attr_accessor :is_active
    attr_accessor :created

    attr_accessor :app_id

    attr_mapping({
      'id' => :id,
      'name' => :name,
      'isInternalGroup' => :is_internal_group,
      'appAdamId' => :app_id,
      'isDefaultExternalGroup' => :is_default_external_group,
 
    
    def add_tester!(tester)
      # This post request creates an account-level tester and then makes it available to the app, or just makes
      # it available to the app if it already exists
      client.create_app_level_tester(app_id: self.app_id,
                                 first_name: tester.first_name,
                                  last_name: tester.last_name,
                                      email: tester.email)
      # This put request adds the tester to the group
      client.post_tester_to_group(group_id: self.id,
                                     email: tester.email,
                                first_name: tester.first_name,
                                 last_name: tester.last_name,
                                    app_id: self.app_id)
    end