delivery: add delivery test

spec/factories/delivery.rb

@@ -0,0 +1,9 @@
+require 'factory_bot'
+
+FactoryBot.define do
+    factory :delivery do
+        supplier { create :supplier }
+        invoice { create :invoice }
+        date { Faker::Date.backward(days: 14) }
+    end
+end

spec/models/delivery_spec.rb

@@ -0,0 +1,23 @@
+require_relative '../spec_helper'
+
+describe Delivery do
+  let(:delivery) { create :delivery }
+  let(:stock_article) { create :stock_article, price: 3 }
+
+  it 'creates new stock_changes' do
+    delivery.new_stock_changes = ([
+      {
+        quantity: 1,
+        stock_article: stock_article
+      },
+      {
+        quantity: 2,
+        stock_article: stock_article
+      }
+    ])
+
+    expect(delivery.stock_changes.last[:stock_article_id]).to be stock_article.id
+    expect(delivery.includes_article?(stock_article)).to be true
+    expect(delivery.sum(:net)).to eq 9
+  end
+end