Rails test failure 500 when I use .includes - ruby-on-rails

Question

I'm developing a small e-commerce and I´ve a problem when I run the tests for my cart controller.
here cart controller
class CartsController < ApplicationController
include CurrentCart #modul current_cart in controllers/concerns
before_action :set_cart, only: [:show, :edit, :update, :destroy]
before_action :set_current_cart, only: [:index]
# GET /carts
# GET /carts.json
def index
respond_to do |format|
format.html { redirect_to #cart, notice: 'Line item was successfully created.' }
format.json { render :show, status: :created, location: #line_item }
end
end
# GET /carts/1
# GET /carts/1.json
def show
end
# GET /carts/new
def new
#cart = Cart.new
end
# GET /carts/1/edit
def edit
end
# POST /carts
# POST /carts.json
def create
#cart = Cart.new(cart_params)
respond_to do |format|
if #cart.save
format.html { redirect_to #cart, notice: 'Cart was successfully created.' }
format.json { render :show, status: :created, location: #cart }
else
format.html { render :new }
format.json { render json: #cart.errors, status: :unprocessable_entity }
end
end
end
# PATCH/PUT /carts/1
# PATCH/PUT /carts/1.json
def update
respond_to do |format|
if #cart.update(cart_params)
format.html { redirect_to #cart, notice: 'Cart was successfully updated.' }
format.json { render :show, status: :ok, location: #cart }
else
format.html { render :edit }
format.json { render json: #cart.errors, status: :unprocessable_entity }
end
end
end
# DELETE /carts/1
# DELETE /carts/1.json
def destroy
#cart.destroy if #cart.id == session[:cart_id]
session[:cart_id] = nil
respond_to do |format|
format.html { redirect_to catalog_index_url, notice: 'Cart was successfully destroyed.' }
format.json { head :no_content }
end
end
private
# Use callbacks to share common setup or constraints between actions.
def set_cart
#cart = Cart.includes(line_items: :product).find(params[:id])
end
# Never trust parameters from the scary internet, only allow the white list through.
def cart_params
params.fetch(:cart, {})
end
end
and here my tests:
require 'test_helper'
class CartsControllerTest < ActionDispatch::IntegrationTest
setup do
#line_item = line_items(:one)
#product = products(:one)
#cart = carts(:one)
end
test "should get index" do
get carts_url
assert_response :success
end
test "should get new" do
get new_cart_url
assert_response :success
end
test "should create cart" do
assert_difference('Cart.count') do
post carts_url, params: { cart: {} }
end
assert_redirected_to cart_url(Cart.last)
end
test "should show cart" do
get cart_url(#cart)
assert_response :success
end
test "should get edit" do
get edit_cart_url(#cart)
assert_response :success
end
test "should update cart" do
patch cart_url(#cart), params: { cart: {} }
assert_redirected_to cart_url(#cart)
end
test "should destroy cart" do
post line_items_url, params: { product_id: products(:one).id }
#cart = Cart.find(session[:cart_id])
assert_difference('Cart.count', -1) do
delete cart_url(#cart)
end
assert_redirected_to catalog_index_url
end
end
here the results:
Failure: CartsControllerTest#test_should_destroy_cart Expected
response to be a <3XX: redirect>, but was a <500: Internal Server
Error>
Failure: CartsControllerTest#test_should_get_edit Expected response
to be a <2XX: success>, but was a <500: Internal Server Error>
Failure: CartsControllerTest#test_should_update_cart Expected
response to be a <3XX: redirect>, but was a <500: Internal Server
Error>
here is the modul current cart for the cartsController:
module CurrentCart
private
def set_current_cart
#cart = Cart.find(session[:cart_id])
rescue ActiveRecord::RecordNotFound
#cart = Cart.create
session[:cart_id] = #cart.id
end
end
I think that the problem is here:
if I remove this in the method set_cart from the cart controller: .includes(line_items: :product) the tests will run perfectly without failure, but I cannot understand why.
(I put the include because otherwise I get this error when I access the cart from the browser:
USE eager loading detected LineItem => [:product] Add to your
finder: :includes => [:product] Call stack
UPDATE:
I found something interesting in the file "test.log" :
Bullet::Notification::UnoptimizedQueryError - user: claudio
DELETE /carts/980190963
AVOID eager loading detected
LineItem => [:product]
Remove from your finder: :includes => [:product]
Call stack
##here there's a path##.rb:45:in `block (2 levels) in <class:CartsControllerTest>'
##here there's a path##:in `block in <class:CartsControllerTest>'