Simplify main method by creating two private methods

Include some unit tests

app/controllers/concerns/address_transformation.rb

@@ -26,22 +26,23 @@ module AddressTransformation
       }.with_indifferent_access[key]
     end
 
-    if address[:state].present?
-      address[:state] = Spree::State.find_by(
-        "LOWER(abbr) = ? OR LOWER(name) = ?",
-        address.dig(:state, :code)&.downcase,
-        address.dig(:state, :name)&.downcase,
-      )
-    end
-
-    if address[:country].present?
-      address[:country] = Spree::Country.find_by(
-        "LOWER(iso) = ? OR LOWER(name) = ?",
-        address.dig(:country, :code)&.downcase,
-        address.dig(:country, :name)&.downcase,
-      )
-    end
+    address[:state] = find_state(address) if address[:state].present?
+    address[:country] = find_country(address) if address[:country].present?
 
     attributes["#{to}_attributes"] = address
   end
+
+  private
+
+  def find_state(address)
+    Spree::State.find_by("LOWER(abbr) = ? OR LOWER(name) = ?",
+                         address.dig(:state, :code)&.downcase,
+                         address.dig(:state, :name)&.downcase)
+  end
+
+  def find_country(address)
+    Spree::Country.find_by("LOWER(iso) = ? OR LOWER(name) = ?",
+                           address.dig(:country, :code)&.downcase,
+                           address.dig(:country, :name)&.downcase)
+  end
 end

spec/controllers/concerns/address_transformation_spec.rb

@@ -0,0 +1,97 @@
+# frozen_string_literal: true
+
+require "spec_helper"
+
+describe AddressTransformation do
+  include AddressTransformation
+
+  describe "#transform_address!" do
+    describe "default cases" do
+      let(:attributes) do
+        { shipping_address: CustomerSchema.address_example,
+          billing_address: CustomerSchema.address_example }
+      end
+
+      let(:wanted_address) do
+        CustomerSchema.address_example.
+          except( :first_name, :last_name, :locality,
+                  :postal_code, :region, :street_address_1, :street_address_2).
+          merge(
+            firstname: "Alice",
+            lastname: "Springs",
+            address1: "1 Flinders Street",
+            address2: "",
+            zipcode: "1234",
+            city: "Melbourne",
+            state: Spree::State.find_by(name: "Victoria"),
+            country: Spree::Country.find_by(name: "Australia"),
+          )
+      end
+
+      it "transforms the shipping_address and the billing_address" do
+        transformed_address = transform_address!(attributes, :shipping_address, :ship_address)
+        expect(transformed_address).to eq(wanted_address)
+        expect(attributes["ship_address_attributes"]).to eq(wanted_address)
+
+        transformed_address = transform_address!(attributes, :billing_address, :bill_address)
+        expect(transformed_address).to eq( wanted_address)
+        expect(attributes["bill_address_attributes"]).to eq(wanted_address)
+      end
+    end
+
+    describe "when the address attributes are nil" do
+      let(:attributes) do
+        { shipping_address: nil,
+          billing_address: nil }
+      end
+
+      it "returns nil" do
+        transformed_address = transform_address!(attributes, :shipping_address, :ship_address)
+        expect(transformed_address).to be_nil
+        expect(attributes["ship_address_attributes"]).to be_nil
+
+        transformed_address = transform_address!(attributes, :billing_address, :bill_address)
+        expect(transformed_address).to be_nil
+        expect(attributes["bill_address_attributes"]).to be_nil
+      end
+    end
+
+    describe "when attributes doesn't contains the searched key" do
+      let(:attributes) do
+        {
+          address: CustomerSchema.address_example,
+        }
+      end
+
+      it "returns nil" do
+        transformed_address = transform_address!(attributes, :shipping_address, :ship_address)
+        expect(transformed_address).to be_nil
+        expect(attributes["ship_address_attributes"]).to be_nil
+      end
+    end
+  end
+
+  describe "#find_state" do
+    it "finds the state" do
+      state = find_state(
+        state: {
+          code: "VIC",
+          name: "Victoria",
+        },
+      )
+      expect(state).to eq(Spree::State.find_by(name: "Victoria"))
+    end
+  end
+
+  describe "#find_country" do
+    it "finds the country" do
+      country = find_country(
+        country: {
+          code: "AU",
+          name: "Australia",
+        },
+      )
+      expect(country).to eq(Spree::Country.find_by(name: "Australia"))
+    end
+  end
+end