books_controller.rb

class BooksController < ApplicationController
  def show
    @book = Book.find(params[:id])
    @reviews = @book.reviews.where(approved: true) || []
  end
end

spec.rb

require 'rails_helper'

RSpec.describe "fill cart -> login -> checkout", :type => :feature, js: true do
  it 'fill cart -> login -> checkout' do
    user = create(:user)
    book_1 = create(:book)
    book_2 = create(:book)
    expect(Book.find(1)).to eq book_1
    
    visit book_path(book_1)
    click_on 'Add to Cart'
    click_on 'Add to Cart'
  end
end