ActiveRecord merge test for order of joins

test.rb

unless File.exists?('Gemfile')
  File.write('Gemfile', <<-GEMFILE)
    source 'https://rubygems.org'
    gem 'rails', github: 'rails/rails'
    gem 'sqlite3'
  GEMFILE

  system 'bundle'
end

require 'bundler'
Bundler.setup(:default)

require 'active_record'
require 'minitest/autorun'
require 'logger'
#require 'debugger'

# 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 :posts do |t|
  end

  create_table :comments do |t|
    t.integer :post_id
    t.string :name
  end
end

class Post < ActiveRecord::Base
  has_many :comments
end

class Comment < ActiveRecord::Base
  belongs_to :post
  scope :fails, -> { 
    parent = Arel::Table.new('other_table')
    joins(self.arel_table.join(parent).join_sources)
  }
  scope :works, -> { 
    parent = Arel::Table.new('other_table')
    joins(self.arel_table.join(parent).join_sources.map(&:to_sql).join(' '))
  }
end

class BugTest < MiniTest::Unit::TestCase
  def test_joins_on_correct_order_fails
    assert_equal Post.joins('INNER JOIN "comments" ON "comments"."post_id" = "posts"."id"').merge(Comment.fails).to_sql, 'SELECT "posts".* FROM "posts" INNER JOIN "comments" ON "comments"."post_id" = "posts"."id" INNER JOIN "other_table"'
  end

  def test_joins_on_correct_order_works
     assert_equal Post.joins(:comments).merge(Comment.fails).to_sql, 'SELECT "posts".* FROM "posts" INNER JOIN "comments" ON "comments"."post_id" = "posts"."id" INNER JOIN "other_table"'
  end

  def test_joins_on_correct_order_works2
     assert_equal Post.joins(:comments).merge(Comment.works).to_sql, 'SELECT "posts".* FROM "posts" INNER JOIN "comments" ON "comments"."post_id" = "posts"."id" INNER JOIN "other_table"'
  end
end