"should get show" controller test failing for Nested resource

Question

I have a User model and a Shoppingcart model where

# user.rb
class User < ActiveRecord::Base
    has_one :shoppingcart
end

and

# shopppingcart.rb
class Shoppingcart < ActiveRecord::Base
    belongs_to :user
end

and I have this in routes.rb:

resources :users do
    resource :shoppingcart
end

and in Shoppingcarts_controller.rb I have

class ShoppingcartsController < ApplicationController
    def show
        @user = User.find(current_user)
        @shoppingcart = @user.build_shoppingcart
    end
end

and within shoppingcarts_controller_test.rb:

require 'test_helper'
class ShoppingcartsControllerTest < ActionController::TestCase
    def setup
        @user = users(:michael)
    end
    test "should get show" do
        puts(@user.name) # => Michael Example
        puts(@user.id) # => 762146111
        get :show # error line
        assert_response :success
    end
end

But when ever I run the test I get ActiveRecord::RecordNotFound: Couldn't find User with 'id'=. When I comment out the error line the error goes away and everything works. As for the non-test code, everything works. I can reach users/1/shoppingcart with no issue, so the problem must be coming from the test itself. How do I make a test for an action to a nested resource?

SessionsHelper.rb:

module SessionsHelper

    # Returns the current logged-in user (if any).
    def current_user
        if (user_id = session[:user_id])
            @current_user ||= User.find_by(id: user_id)
        elsif (user_id = cookies.signed[:user_id])
            user = User.find_by(id: user_id)
            if user && user.authenticated?(:remember, cookies[:remember_token])
                log_in user
                @current_user = user
            end
        end
    end
end 

Answer 1

find method requires primary key of the particular user from Users table, not the user itself. Primary key is id, so you need to change this line in your controller.

@user = User.find(params[:user_id])