Failure/Error: Unable to find matching line from backtrace
ArgumentError:
  comparison of Symbol with Module Failed

我有以下控制器测试

require 'spec_helper'

describe PeopleController,type: :controller do
  subject { response }

  describe :index do
    before { get :index }

    it { should_not be_success }
    it { should have_http_status '401' }
  end
end

任何想法可能导致错误？