after_initialize and AR callbacks

gistfile1.rb

# Activate the gem you are reporting the issue against.
gem 'activerecord', '4.2.0'
require 'active_record'
require 'minitest/autorun'
require 'logger'
require 'byebug'

# 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::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
    t.text :content
  end
end

class Post < ActiveRecord::Base
  has_many :comments
end

class Comment < ActiveRecord::Base
  belongs_to :post
  after_initialize :set_default

  def set_default
    content ||= 'default text' if new_record?
  end
end

class BugTest < Minitest::Test
  def test_successfully_adds_default
    comment = Comment.new
    assert !comment.content.nil?
  end
end