test application controller method

application_controller_test.rb

class ApplicationControllerTest < ActionController::TestCase
  def setup
    # create and initialize anonymous controller
    @controller = Class.new(ApplicationController) do
      def index
        # what goes here all depends on the situation and the method your trying to test 
      end
    end::new
  end

  test "my test" do
    get :index
  end
end