attr_accessibleのspec

1.spec/support/be_accessible_matcher.rb を作成

be_accessible_matcher.rb

RSpec::Matchers.define :be_accessible do |attribute|
  match do |response|
    response.class.accessible_attributes.include?(attribute)
  end
  description { "be accessible :#{attribute}" }
  failure_message_for_should { ":#{attribute} should be accessible" }
  failure_message_for_should_not { ":#{attribute} should not be accessible" }
end

2.モデルのスペックを作成（Userの場合）

user_spec.rb

# encoding: utf-8
require 'spec_helper'

describe User do
  context "attr_accessible が設定されている" do

    before do
      @user = User.new
      @accessible = [:firstname, :lastname, :email]
    end

    it "すべてのカラムをチェック" do
      @event.class.column_names.each do |name|
        if @accessible.include?(name.to_sym) then
          @event.should be_accessible name.to_sym
        else
          @event.should_not be_accessible name.to_sym
        end
      end
    end

  end
end

参考
RSpecでmodelのattr_accessibleをテストする