factory girl は mass assignment を回避してデータを作れるか？ YES

factory_girl_massassignment.rb

require "active_record"
require "sqlite3"

ActiveRecord::Base.configurations = {'test' => {:adapter => 'sqlite3', :database => ':memory:'}}
ActiveRecord::Base.establish_connection('test')

class CreateAllTables < ActiveRecord::Migration
  def self.up
    create_table :locales do |t|
      t.string :name
      t.integer :key
    end
  end
end

CreateAllTables.up

class Locale < ActiveRecord::Base
  attr_accessible :name

  validates :name, presence: true
  validates :key, presence: true
end

u = Locale.new(name: "name", key: 10)
u.save
u.errors.full_messages          # => ["Key can't be blank"]

require "factory_girl"

FactoryGirl.define do
  factory :locale do
    name "Akihiro Matsumura"
    key 29
  end
end

fu = FactoryGirl.create(:locale)
fu.valid?                       # => true
fu.attributes                   # => {"id"=>1, "name"=>"Akihiro Matsumura", "key"=>29}