CanCanCan Issue

main.rb

begin
  require 'bundler/inline'
rescue LoadError => e
  $stderr.puts 'Bundler version 1.10 or later is required. Please update your Bundler'
  raise e
end

gemfile(true) do
  source 'https://rubygems.org'
  gem 'rails', '7.1'  # use correct rails version
  gem 'cancancan', '3.5.0', require: false # use correct cancancan version
  gem 'sqlite3', '~> 1.4' # use another DB if necessary
end

require 'active_record'
require 'action_controller'
require 'cancancan'
require 'cancan/model_adapters/active_record_adapter'
require 'cancan/model_adapters/active_record_4_adapter'
require 'minitest/autorun'
require 'logger'

# This connection will do for database-independent bug reports.
ActiveRecord::Base.establish_connection(adapter: 'sqlite3', database: ':memory:')
ActiveRecord::Base.logger = Logger.new(STDOUT)

# create your tables here
ActiveRecord::Schema.define do
  create_table :books, force: true  do |t|
    t.integer :user_id
    t.string :title
    t.string :secret_attribute
  end

  create_table :users, force: true  do |t|
    t.string :name
  end
end

class Book < ActiveRecord::Base
  belongs_to :user
end

class User < ActiveRecord::Base
  has_many :books
end

class Ability
  include CanCan::Ability

  def initialize(user)
    can :read, Book, [:id, :title], user: user
  end
end

class TestApp < Rails::Application
  config.root = File.dirname(__FILE__)
  config.session_store :cookie_store, key: "cookie_store_key"
  secrets.secret_token    = "secret_token"
  secrets.secret_key_base = "secret_key_base"

  config.logger = Logger.new($stdout)
  Rails.logger  = config.logger

  routes.draw do
    resources :books
  end
end

class BooksController < ActionController::Base
  include CanCan::ControllerAdditions

  load_and_authorize_resource :book
  
  def index
    render json: @books
  end
  
  private
  
  def current_user
    User.first
  end
end

class ExampleControllerTest < ActionController::TestCase

  setup do
    @controller = BooksController.new
    @routes = Rails.application.routes
  end

  def test_action
    user_1 = User.create(name: 'John Doe')
    user_2 = User.create(name: 'Jane Roe')
    book_1 = user_1.books.create!(title: 'Harry Potter and the Chamber of Secrets', secret_attribute: 'Tom Riddle')
    book_2 = user_2.books.create!(title: 'Lord of the Rings', secret_attribute: 'My Precious')

    get :index
    assert_equal [{ 'id' => book_1.id, 'title' => 'Harry Potter and the Chamber of Secrets' }], response.parsed_body
  end
end