require 'spec_helper'

describe RootController do

  describe "GET 'index'" do
    it "returns http success" do
      get 'index'
      expect(response).to be_success
    end
  end

end

require 'spec_helper'

describe RootController, :type => :controller do

  describe "GET 'index'" do
    it "returns http success" do
      get 'index'
      expect(response).to be_success
    end
  end

end

Test for root controller in generated new app
[FIX] Test for root controller in generated new app