issue 18062

test_ar.rb

system 'rm Gemfile' if File.exist?('Gemfile')
File.write('Gemfile', <<-GEMFILE)
  source 'https://rubygems.org'
  gem 'activerecord',
    '4.2.0.rc3'
    # '4.1.8'
    # '4.0.12'
    # '3.2.21'
  gem 'sqlite3'
GEMFILE

system 'bundle install'

require 'byebug'
require 'bundler'
Bundler.setup(:default)

require 'active_record'
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)

ActiveRecord::Schema.define do
  create_table :businesses do |t|
    t.string :type
  end
end

class Business < ActiveRecord::Base
end

class Foundation < Business
  attr_accessor :lobbyist
end

class Company < Business
end

# class BugTest < Minitest::Test
class BugTest < MiniTest::Unit::TestCase
  def setup
    companya = Company.create
    companyb = Company.create
    foundationa = Foundation.create
    foundationb = Foundation.create
  end

  def test_association_build_sti_1
    assert_equal Business, Business.new.class
  end

  def test_association_build_sti_2
    assert_equal Business, Business.where(type: 'Business').build.class
  end

  def test_association_build_sti_3
    assert_equal Company, Business.where(type: 'Company').build.class
  end

  def test_association_build_sti_4
    assert_equal Foundation, Business.where(type: 'Foundation').build.class
  end

  def test_association_build_sti_5
    foundation = Business.where(type: 'Foundation', lobbyist: true).build
    assert_equal Foundation, foundation.class
    assert_not_nil foundation.lobbyist
  end

  def test_association_build_sti_6
    assert_equal Company, Business.new(type: 'Company').class
  end

  def test_association_build_sti_7
    assert_equal Foundation, Business.new(type: 'Foundation').class
  end

  def test_association_build_sti_8
    assert_equal Foundation, Business.new(type: 'Foundation', lobbyist: true).class
  end
end

ref rails/rails#18062