Bring shipping_method factory from spree_core and merge with modification

spec/factories/shipping_method_factory.rb

@@ -1,4 +1,34 @@
 FactoryBot.define do
+  factory :base_shipping_method, class: Spree::ShippingMethod do
+    zones { [] }
+    name 'UPS Ground'
+
+    distributors { [Enterprise.is_distributor.first || FactoryBot.create(:distributor_enterprise)] }
+    display_on ''
+
+    before(:create) do |shipping_method, evaluator|
+      shipping_method.shipping_categories << (Spree::ShippingCategory.first || create(:shipping_category))
+    end
+
+    trait :flat_rate do
+      transient { amount 1 }
+      calculator { build(:calculator_flat_rate, preferred_amount: amount) }
+    end
+
+    trait :per_item do
+      transient { amount 1 }
+      calculator { build(:calculator_per_item, preferred_amount: amount) }
+    end
+
+    factory :shipping_method, class: Spree::ShippingMethod do
+      association(:calculator, factory: :calculator, strategy: :build)
+    end
+
+    factory :free_shipping_method, class: Spree::ShippingMethod do
+      association(:calculator, factory: :no_amount_calculator, strategy: :build)
+    end
+  end
+
   factory :shipping_method_with, parent: :shipping_method do
     trait :delivery do
       require_ship_address { true }
@@ -36,21 +66,3 @@ FactoryBot.define do
     end
   end
 end
-
-FactoryBot.modify do
-  factory :shipping_method, parent: :base_shipping_method do
-    distributors { [Enterprise.is_distributor.first || FactoryBot.create(:distributor_enterprise)] }
-    display_on ''
-    zones { [] }
-
-    trait :flat_rate do
-      transient { amount 1 }
-      calculator { build(:calculator_flat_rate, preferred_amount: amount) }
-    end
-
-    trait :per_item do
-      transient { amount 1 }
-      calculator { build(:calculator_per_item, preferred_amount: amount) }
-    end
-  end
-end