Persistance#become bug

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 'arel', github: 'rails/arel'
  gem 'rails', github: 'rails/rails'
  gem 'sqlite3'
end

# Activate the gem you are reporting the issue against.
require 'active_record'
require 'minitest/autorun'

# Ensure backward compatibility with Minitest 4
Minitest::Test = MiniTest::Unit::TestCase unless defined?(Minitest::Test)

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

ActiveRecord::Schema.define do
  create_table :users, force: true do |t|
    t.string :name
    t.text :data, default: '{}'
    t.string :type
  end
end

class User < ActiveRecord::Base
  store :data, coder: JSON
  validates :name, presence: true
end

class Admin < User
  store_accessor :data, :permissions
  validates :permissions, presence: true
end

class BugTest < ActiveSupport::TestCase
  def test_becomes_errors
    user = User.new
    assert_not user.valid?
    admin = user.becomes(Admin)
    admin.name = 'admin'
    # This raises NoMethodError: undefined method `permissions' for ...
    assert_not admin.valid?
  end
end