Building CanCan abilities incrementally (most edits are minor, I removed direct use of Class at some point)

ability_spec.rb

require 'spec_helper'

require 'spec/environments/mongoid'

require_unless_rails_loaded 'app/models/ability'

describe Ability do
  let(:user) { mock(User) }

  describe ".build" do
    let(:ability_builder_1) {
      Ability::AbilityBuilder.new do
        def build
          can(:throw, Object)
        end
      end
    }

    let(:ability_builder_2) {
      Ability::AbilityBuilder.new do
        def build
          can(:worship, Object)
          cannot(:throw, Object)
        end
      end
    }

    let(:ability_builder_with_user) {
      Ability::AbilityBuilder.new do
        def build
          if user.admin?
            can(:administrate, Object)
          else
            can(:beg_for, Object)
          end
        end
      end
    }

    context "no abilities" do
      subject { Ability.build(user) }

      describe "#can?" do
        it "exists" do
          subject.can?(:eat, Object).should be_false
        end
      end
    end

    context "an ability builder" do
      subject { Ability.build(user, ability_builder_1) }

      describe "#can?" do
        it "is driven by the ability builders" do
          subject.should be_able_to(:throw, Object)
        end
      end
    end

    context "two ability builders" do
      subject { Ability.build(user, ability_builder_1, ability_builder_2) }

      describe "#can?" do
        it "uses all ability builders" do
          subject.should be_able_to(:worship, Object)
        end

        it "uses ability builders in the order they were provided" do
          subject.should_not be_able_to(:throw, Object)
        end
      end
    end

    context "an ability builder that depends on the user" do
      subject { Ability.build(user, ability_builder_with_user) }

      context "when the user is an administrator" do
        before(:each) do
          user.stub(admin?: true)
        end

        it "uses the user" do
          subject.should be_able_to(:administrate, Object)
          subject.should_not be_able_to(:beg_for, Object)
        end
      end

      context "when the user is not an administrator" do
        before(:each) do
          user.stub(admin?: false)
        end

        it "uses the user" do
          subject.should be_able_to(:beg_for, Object)
          subject.should_not be_able_to(:administrate, Object)
        end
      end
    end
  end
end