missing required keys: [:user_id]

gistfile1.rb

# Routes
                Prefix Verb   URI Pattern                                      Controller#Action
           sidekiq_web        /sidekiq                                         Sidekiq::Web
                  root GET    /                                                high_voltage/pages#show {:id=>"home"}
    user_bank_accounts GET    /users/:user_id/bank_accounts(.:format)          bank_accounts#index
                       POST   /users/:user_id/bank_accounts(.:format)          bank_accounts#create
 new_user_bank_account GET    /users/:user_id/bank_accounts/new(.:format)      bank_accounts#new
edit_user_bank_account GET    /users/:user_id/bank_accounts/:id/edit(.:format) bank_accounts#edit
     user_bank_account GET    /users/:user_id/bank_accounts/:id(.:format)      bank_accounts#show
                       PATCH  /users/:user_id/bank_accounts/:id(.:format)      bank_accounts#update
                       PUT    /users/:user_id/bank_accounts/:id(.:format)      bank_accounts#update
                       DELETE /users/:user_id/bank_accounts/:id(.:format)      bank_accounts#destroy
         user_products GET    /users/:user_id/products(.:format)               products#index
                       POST   /users/:user_id/products(.:format)               products#create
      new_user_product GET    /users/:user_id/products/new(.:format)           products#new
     edit_user_product GET    /users/:user_id/products/:id/edit(.:format)      products#edit
          user_product GET    /users/:user_id/products/:id(.:format)           products#show
                       PATCH  /users/:user_id/products/:id(.:format)           products#update
                       PUT    /users/:user_id/products/:id(.:format)           products#update
                       DELETE /users/:user_id/products/:id(.:format)           products#destroy
                 users GET    /users(.:format)                                 users#index
                       POST   /users(.:format)                                 users#create
              new_user GET    /users/new(.:format)                             users#new
             edit_user GET    /users/:id/edit(.:format)                        users#edit
                  user GET    /users/:id(.:format)                             users#show
                       PATCH  /users/:id(.:format)                             users#update
                       PUT    /users/:id(.:format)                             users#update
                       DELETE /users/:id(.:format)                             users#destroy
                 login GET    /login(.:format)                                 sessions#new
            post_login POST   /login(.:format)                                 sessions#create
                logout DELETE /logout(.:format)                                sessions#destroy
                  page GET    /*id                                             high_voltage/pages#show

# app/controllers/products_controller.rb
class ProductsController < ApplicationController
  ...

  def create
    @user = Product.new(product_params)

    if @user.save
      redirect_to user_products_path(current_user), notice: 'Product has been uploaded'
    else
      render :new
    end
  end

  ...

  private

  def product_params
    params.require(:product).permit(:status, :name, :description, :price_cents, :price_currency)
  end
end

# spec/controllers/products_controller_spec.rb
require 'rails_helper'

describe ProductsController do
  let(:user) { create :user }

  describe 'GET new' do
    before { get :new, user_id: user.id }

    it 'assigns @user' do
      expect(assigns(:user)).to be_a Product
    end
  end

  describe 'POST create' do
    context 'with valid params' do
      let(:valid_product) { attributes_for :product }

      it 'redirects to user_products_path' do
        post :create, user_id: user.id, product: valid_product # this is the line it breaks on
        expect(response).to redirect_to(user_products_path(user))
      end
    end

    context 'with invalid params' do
      let(:invalid_product) { attributes_for(:product, name: '') }

      it 'renders :new' do
        post :create, user_id: user.id, product: invalid_product # this works just fine
        expect(response).to render_template(:new)
      end
    end
  end
end

# RSpec output

# ActionController::UrlGenerationError:
  # No route matches {:action=>"index", :controller=>"products", :user_id=>nil} missing required keys: [:user_id]