使用rspec测试控制器中的销毁方法

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.