How to test policy scopes

let(:user)         { FactoryGirl.create :user }
let(:manager)      { FactoryGirl.create :manager }
let(:managed_user) { FactoryGirl.create :user, manager_id: manager.id }

before do
  sign_in manager
end

it "should return only his managed users" do     
  expect(UserPolicy::Scope.new(manager, User.all).resolve).to include(managed_user)
  expect(UserPolicy::Scope.new(manager, User.all).resolve).not_to include(user)
end