Adds zone_with_state_member to zone factory

And make zone factories more flexible.

spec/factories/zone_factory.rb

@@ -7,10 +7,15 @@ FactoryBot.define do
   end
 
   factory :zone_with_member, parent: :zone do
-    default_tax { true }
-
-    after(:create) do |zone|
-      Spree::ZoneMember.create!(zone: zone, zoneable: Spree::Country.find_by(name: 'Australia'))
+    transient do
+      member { Spree::Country.find_by(name: "Australia") }
     end
+
+    default_tax { true }
+    zone_members { [Spree::ZoneMember.new(zoneable: member)] }
+  end
+
+  factory :zone_with_state_member, parent: :zone_with_member do
+    member { Spree::State.find_by(name: "Victoria") }
   end
 end