I added a column called notify in one of my tables and all the tests started failing. In particulr factory_girl started blowing up. Here is the exception I was getting.

>> User.new.save
  ArgumentError: wrong number of arguments (1 for 0)
	from /Library/Ruby/Gems/1.8/gems/activerecord-2.3.2/lib/active_record/callbacks.rb:350:in `notify'
	from /Library/Ruby/Gems/1.8/gems/activerecord-2.3.2/lib/active_record/callbacks.rb:350:in `callback'
	from /Library/Ruby/Gems/1.8/gems/activerecord-2.3.2/lib/active_record/callbacks.rb:267:in `create'
	from /Library/Ruby/Gems/1.8/gems/activerecord-2.3.2/lib/active_record/base.rb:2868:in   
       `create_or_update_without_callbacks'

This is the code ActiveRecord has

# lib/active_record/callbacks.rb

private
def callback(method)
  result = run_callbacks(method) { |result, object| false == result }

  if result != false && respond_to_without_attributes?(method)
    result = send(method)
  end

  notify(method)

  return result
end

Since User has a column called ‘notify’, the notify method defined in callbacks.rb is getting overridden by @user.notify.

This code was tested with Rails 2.3.2