Rails Rspec - How to set polymorphic has_many association - ruby-on-rails

Question

I have a model (payment) that belongs to another model (event), via a polymorphic association.
Some tests are failing because the owner model (event) is accessed by the payment model in validations, but the event is returning nil. All the features work fine when testing app directly in the browser.
I added some more comments to payment.rb below.
I've tried defining the association in the factories, but no luck.
What is the best way to set up this association in the spec?
# models/event.rb
class Event < ApplicationRecord
has_many :payments, as: :payable, dependent: :destroy
end
# models/payment.rb
class Payment < ApplicationRecord
belongs_to :payable, polymorphic: true
validate :amount_is_valid
def amount_is_valid
if amount.to_i > payable.balance.to_i
errors.add(:amount, "can't be higher than balance")
end
end
end
Both examples in this spec are failing.
# spec/models/payment_spec.rb
require 'rails_helper'
RSpec.describe Payment, type: :model do
let!(:event) { FactoryBot.create(:event, event_type: 'test', total: 10000, balance: 10000) }
let!(:user) {FactoryBot.create(:user)}
let!(:payment) {
FactoryBot.build(:payment,
amount: 300,
method: 'cash',
payer_id: user.id,
payable_id: event.id,
status: 1,
)
}
describe 'Association' do
it do
# This will fail with or without this line
payment.payable = event
is_expected.to belong_to(:payable)
end
end
# Validation
describe 'Validation' do
describe '#amount_is_valid' do
it 'not charge more than event balance' do
# This will make the test pass. The actual spec has a lot more examples though,
# would rather just set the association once.
# payment.payable = event
payment.amount = 5000000
payment.validate
expect(payment.errors[:amount]).to include("can't be higher than balance")
end
end
end
end
Output
# bundle exec rspec spec/models/payment_spec.rb
Randomized with seed 42748
Payment
Association
should belong to payable required: true (FAILED - 1)
Validation
#amount_is_valid
not charge more than event balance (FAILED - 2)
Failures:
1) Payment Association should belong to payable required: true
Failure/Error: if amount.to_i > payable.balance.to_i
NoMethodError:
undefined method `balance' for nil:NilClass
# ./app/models/payment.rb:9:in `amount_is_valid'
# ./spec/models/payment_spec.rb:23:in `block (3 levels) in <top (required)>'
# ./spec/rails_helper.rb:80:in `block (3 levels) in <top (required)>'
# ./spec/rails_helper.rb:79:in `block (2 levels) in <top (required)>'
# ./spec/spec_helper.rb:108:in `block (2 levels) in <top (required)>'
2) Payment Validation #amount_is_valid not charge more than event balance
Failure/Error: if amount.to_i > payable.balance.to_i
NoMethodError:
undefined method `balance' for nil:NilClass
# ./app/models/payment.rb:9:in `amount_is_valid'
# ./spec/models/payment_spec.rb:39:in `block (4 levels) in <top (required)>'
# ./spec/rails_helper.rb:80:in `block (3 levels) in <top (required)>'
# ./spec/rails_helper.rb:79:in `block (2 levels) in <top (required)>'
# ./spec/spec_helper.rb:108:in `block (2 levels) in <top (required)>'
Top 2 slowest examples (0.29972 seconds, 71.6% of total time):
Payment Association should belong to payable required: true
0.28796 seconds ./spec/models/payment_spec.rb:18
Payment Validation #amount_is_valid not charge more than event balance
0.01176 seconds ./spec/models/payment_spec.rb:32
Finished in 0.4186 seconds (files took 4.31 seconds to load)
2 examples, 2 failures
Failed examples:
rspec ./spec/models/payment_spec.rb:18 # Payment Association should belong to payable required: true
rspec ./spec/models/payment_spec.rb:32 # Payment Validation #amount_is_valid not charge more than event balance
Update
Passing specs based on Schwern's feedback.
Still using a custom validation for amount, because balance is a field on the associated payable, not the payment (couldn't find a way to access an associated model from inside a built-in validation helper)
# payment.rb
class Payment < ApplicationRecord
belongs_to :payable, polymorphic: true
validates :payable, presence: true
validate :amount_is_valid
def amount_is_valid
if amount > payable.balance
errors.add(:amount, "can't be greater than balance")
end
end
end
# spec/models/payment_spec.rb
require 'rails_helper'
RSpec.describe Payment, type: :model do
let(:event) { FactoryBot.create(:event, event_type: 'test', total: 10000, balance: 10000) }
let(:user) {FactoryBot.create(:user)}
let(:payment) {
FactoryBot.build(:payment,
amount: 300,
method: 'cash',
payer_id: user.id,
payable: event,
status: 1,
)
}
describe '#payable' do
it 'is an Event' do
expect(payment.payable).to be_a(Event)
end
end
describe '#amount' do
context 'amount is higher than balance' do
before {
payment.amount = payment.payable.balance + 1
}
it 'is invalid' do
payment.validate
expect(payment.errors[:amount]).to include("can't be greater than balance")
end
end
end
end

Answer 1

Your first test is not failing where you think it is. It's failing on the next line, is_expected.to belong_to(:payable).
You're setting payment, but you're testing the implicitly defined subject which will be Payment.new.
is_expected.to belong_to(:payable)
Is equivalent to...
expect(subject).to belong_to(:payable)
And since you have no defined subject this is...
expect(Payment.new).to belong_to(:payable)
Payment.new does not have payable defined and so the amount_is_valid validation errors.
To fix this, test payment directly. And I would suggest staying away from subject while you're learning RSpec. And you should not have to set payment.event, it's already set in the factory.
describe 'Association' do
expect(payment).to belong_to(:payable)
end
But I'm not aware of a belong_to matcher. You should not be directly checking implementation, but rather its behavior. The behavior you want is for payment.payable to return a Payable.
describe '#payable' do
it 'is a Payable' do
expect(payment.payable).to be_a(Payable)
end
end
The second failure is because you have incorrectly initialized your Payment. You're passing in payable_id: event.id but that does not set payable_type. Without payable_type it doesn't know what class the ID is for.
Instead, pass the objects in directly.
let!(:payment) {
FactoryBot.build(:payment,
amount: 300,
method: 'cash',
payer: user,
payable: event,
status: 1,
)
}
Some more general cleanups...
let! will always run the block whether it's used or not. Unless you specifically need that, use let and the blocks will run as needed.
You expect payable to exist, so validate the presence of payable.
Use the built in numericality validator on amount.
class Payment < ApplicationRecord
belongs_to :payable, polymorphic: true
validates :payable, presence: true
validates :amount, numericality: {
less_than_or_equal_to: balance,
message: "must be less than or equal to the balance of #{balance}"
}
end
require 'rails_helper'
RSpec.describe Payment, type: :model do
let(:event) {
create(:event, event_type: 'test', total: 10000, balance: 10000)
}
let(:user) { create(:user) }
let(:payment) {
build(:payment,
amount: 300,
method: 'cash',
payer: user,
payable: event,
status: 1
)
}
# It's useful to organize tests by method.
describe '#payable' do
it 'is a Payable' do
expect(payment.payable).to be_a(Payable)
end
end
describe '#amount' do
# Contexts also help organize and name your tests.
context 'when the amount is higher than the payable balance' do
# This code will run before each example.
before {
# Rather than hard coding numbers, make your tests relative.
# If event.balance changes the test will still work.
payment.amount = payment.payable.balance + 1
}
it 'is invalid' do
expect(payment.valid?).to be false
expect(payment.errors[:amount]).to include("must be less than or equal to")
end
end
end
end