Confused about default behavior of model initializer - ruby-on-rails

Question

Given the following...
Model:
class Equipment < ApplicationRecord
belongs_to :user
end
Controller:
class EquipmentController < ApplicationController
before_action :set_equipment, only: %i[ show edit update destroy ]
# GET /equipment/new
def new
#equipment = Equipment.new
end
# POST /equipment or /equipment.json
def create
#equipment = Equipment.new(equipment_params)
respond_to do |format|
if #equipment.save
format.html { redirect_to [#equipment.user, #equipment], notice: "Equipment was successfully created." }
format.json { render :show, status: :created, location: #equipment }
else
format.html { render :new, status: :unprocessable_entity }
format.json { render json: #equipment.errors, status: :unprocessable_entity }
end
end
end
Test:
class EquipmentControllerTest < ActionDispatch::IntegrationTest
setup do
#equipment = equipment(:one)
sign_in_as(#equipment.user)
end
test "should get new" do
get new_user_equipment_url(#equipment.user.id)
assert_response :success
end
My test fails here, because equipment.user is null.
<%= form_with(model: [equipment.user, equipment]) do |form| %>
However, when I visit the corresponding URL in the development environment in the browser, it works. Debugging the development environment, the Equipment.new sets the user on the new equipment object. However, when running the test, the user is not set.
Making this change in the controller fixes the issue, but I don't understand the difference in behavior between the integration test and using the browser. Can someone explain?
#equipment = Equipment.new user: Current.user

Answer 1

I think this would be a lot less confusing if you wrote the test properly:
class EquipmentControllerTest < ActionDispatch::IntegrationTest
setup do
#user = users(:one)
sign_in_as(#user)
end
test "should get new" do
get new_user_equipment_url(#user)
assert_response :success
end
end
You should not use the equipment fixture when you're testing the new/create action - after all what your test is supposed to cover is the form for a completely new resource. The equipment fixture would be used when showing and updating an existing equipment.
Then I think you're falling for a classic trap and confusing the #equipment instance variable in your test and the instance variable in your controller with the same name.
Remember that your test and the controller are completely separate instances of different classes - sometimes even running in a completely different processes. Data doesn't just magically teleport itself from the test to the controller - it has to be passed through parameters or be loaded from the database.
#equipment in your controller is just a new Equipment instance that you have created there which doesn't have a user assigned. Thats why you need to assign the user.
Note that unless your users need to be able to create equipment for other users you don't actually need to have a nested route like this. You could just use GET /equipment/new and fetch the user from the session (or a token) instead of a parameter.
For example given a typical Devise setup you would do:
class User < ApplicationRecord
has_many :equipment
end
class EquipmentController < ApplicationController
before_action :set_equipment, only: %i[ show edit update destroy ]
before_action :authenticate_user! # ensure that a user is logged in.
# POST /equipment or /equipment.json
def create
#equipment = current_user.equipment.new(equipment_params)
respond_to do |format|
if #equipment.save
format.html { redirect_to #equipment, notice: "Equipment was successfully created." }
format.json { render :show, status: :created, location: #equipment }
else
format.html { render :new, status: :unprocessable_entity }
format.json { render json: #equipment.errors, status: :unprocessable_entity }
end
end
end