Create a mailer preview for the shipped email

Available on http://localhost:3000/rails/mailers/spree/shipment/shipped

spec/mailers/previews/shipment_preview.rb

@@ -0,0 +1,11 @@
+# frozen_string_literal: true
+
+require 'open_food_network/scope_variant_to_hub'
+
+module Spree
+  class ShipmentPreview < ActionMailer::Preview
+    def shipped
+      ShipmentMailer.shipped_email(Shipment.last)
+    end
+  end
+end