Add first test case for ProductSet

This covers creation and update of a product.

spec/models/spree/product_set_spec.rb

@@ -0,0 +1,65 @@
+require 'spec_helper'
+
+describe Spree::ProductSet do
+  describe '#save' do
+    context 'when passing :collection_attributes' do
+      let(:product_set) do
+        described_class.new(collection_attributes: collection_hash)
+      end
+
+      context 'when the product does not exist yet' do
+        let(:collection_hash) do
+          {
+            0 => {
+              product_id: 11,
+              name: 'a product',
+              price: 2.0,
+              supplier_id: create(:enterprise).id,
+              primary_taxon_id: create(:taxon).id,
+              unit_description: 'description',
+              variant_unit: 'items',
+              variant_unit_name: 'bunches'
+            }
+          }
+        end
+
+        it 'creates it with the specified attributes' do
+          product_set.save
+
+          expect(Spree::Product.last.attributes)
+            .to include('name' => 'a product')
+        end
+      end
+
+      context 'when the product does exist' do
+        let!(:product) do
+          create(
+            :simple_product,
+            variant_unit: 'items',
+            variant_unit_scale: nil,
+            variant_unit_name: 'bunches'
+          )
+        end
+
+        let(:collection_hash) do
+          {
+            0 => {
+              id: product.id,
+              variant_unit: 'weight',
+              variant_unit_scale: 1
+            }
+          }
+        end
+
+        it 'updates all the specified product attributes' do
+          product_set.save
+
+          expect(product.reload.attributes).to include(
+            'variant_unit' => 'weight',
+            'variant_unit_scale' => 1
+          )
+        end
+      end
+    end
+  end
+end