add specs

app/jobs/notify_ordergroup_invoice_job.rb

@@ -0,0 +1,12 @@
+class NotifyOrdergroupInvoiceJob < ApplicationJob
+    def perform(ordergroup_invoice)
+      ordergroup = ordergroup_invoice.multi_group_order.ordergroup
+      ordergroup.users.each do |user|
+        ordergroup_invoice.update!(email_sent_at: Time.current)
+        Mailer.deliver_now_with_user_locale user do
+          Mailer.ordergroup_invoice(ordergroup_invoice, user)
+        end
+      end
+    end
+  end
+