gistfile1.rb

require 'active_record'
require 'minitest/autorun'
require 'logger'

ActiveRecord::Base.establish_connection(adapter: 'sqlite3', database: ':memory:')
ActiveRecord::Base.logger = Logger.new(STDOUT)

ActiveRecord::Schema.define do
  create_table :posts, force: true do |t|
  end

  create_table :comments, force: true do |t|
    t.integer :post_id
  end
end

class Post < ActiveRecord::Base
end

# 1. Add an association to the child class
class FancyPost < Post
  belongs_to :author
end

# 2. Add an association to the parent, which the child should inherit
Post.class_eval do
  has_many :comments
end

class Comment < ActiveRecord::Base
end

class BugTest < Minitest::Test
  def test_association_stuff
    post = FancyPost.new

    # 3. Access the association --> ActiveRecord::AssociationNotFoundError
    post.comments << Comment.new
    post.save!

    assert_equal 1, Comment.count
  end
end