Destroy method in testing controller with rspec - ruby-on-rails

Question

I have a Transaction model, in which I have the following scope :
scope :ownership, -> { where property: true }
I made some tests of the controller (thanks to M. Hartl). There they are :
require 'spec_helper'
describe TransactionsController do
let(:user) { FactoryGirl.create(:user) }
let(:product) { FactoryGirl.create(:givable_product) }
before { be_signed_in_as user }
describe "Ownerships" do
describe "creating an ownership with Ajax" do
it "should increment the Ownership count" do
expect do
xhr :post, :create, transaction: { property: true, user_id: user.id, product_id: product.id }
end.to change(Transaction.ownership, :count).by(1)
end
it "should respond with success" do
xhr :post, :create, transaction: { property: true, user_id: user.id, product_id: product.id }
expect(response).to be_success
end
end
describe "destroying an ownership with Ajax" do
let(:ownership) { user.transactions.ownership.create(product_id: product.id, user_id: user.id) }
it "should decrement the Ownership count" do
expect do
xhr :delete, :destroy, id: ownership.id
end.to change(Transaction.ownership, :count).by(-1)
end
it "should respond with success" do
xhr :delete, :destroy, id: ownership.id
expect(response).to be_success
end
end
end
end
And there is the destroy method of my Transaction controller :
def destroy
#transaction = Transaction.find(params[:id])
#property = #transaction.property
#product = #transaction.product
#transaction.destroy
respond_to do |format|
format.html { redirect_to #product }
format.js
end
end
But when I run the tests, one of them fails, and I don't understand how or why :
1) TransactionsController Ownerships destroying an ownership with Ajax should decrement the Ownership count
Failure/Error: expect do
count should have been changed by -1, but was changed by 0
# ./spec/controllers/transactions_controller_spec.rb:31:in `block (4 levels) in <top (required)>'
Can you help me about it ?

Answer 1

You can use 'let!'.
About 'let' and 'let!': https://www.relishapp.com/rspec/rspec-core/v/2-6/docs/helper-methods/let-and-let

Answer 2

From the RSpec documentation there's a difference between let and let! (see here);
Use let to define a memoized helper method. The value will be cached
across multiple calls in the same example but not across examples.
Note that let is lazy-evaluated: it is not evaluated until the first
time the method it defines is invoked. You can use let! to force the
method's invocation before each example.
In your destroy method use let!(:ownership) so that the ownership object is not cached after it is destroyed.