let(:question) { create :question }
    ....
    it 'redirect to show view' do
        post :create, params: { question: attributes_for(:question) }
        expect(response).to redirect_to(question_path(assigns(:question)))
      end

FactoryBot.define do
  factory :question, class: "Question" do
    id { rand(10000) }
    title { "MyString" }
    body { "MyText" }
    user
  end
end

(byebug) question
#<Question id: 7317, title: "MyString", body: "MyText", created_at: "2019-07-07 09:27:15", updated_at: "2019-07-07 09:27:15", user_id: 7>
(byebug) assigns question
nil
(byebug) assigns :question
#<Question id: nil, title: "MyString", body: "MyText", created_at: nil, updated_at: nil, user_id: nil>

Failure/Error: expect(response).to redirect_to(question_path(assigns(:question)))
     
     ActionController::UrlGenerationError:
       No route matches {:action=>"show", :controller=>"questions", :id=>nil}, missing required keys: [:id]