Split migration into two parts for easier testing

db/migrate/20220105085729_split_customers_name.rb

@@ -1,34 +1,13 @@
 # frozen_string_literal: true
 
 class SplitCustomersName < ActiveRecord::Migration[6.1]
-  class SpreeAddress < ApplicationRecord
-  end
-
-  class Customer < ApplicationRecord
-    belongs_to :bill_address, class_name: "SpreeAddress"
-  end
-
   def up
     add_column :customers, :first_name, :string, null: false, default: ""
     add_column :customers, :last_name, :string, null: false, default: ""
-
-    migrate_customer_name_data!
   end
 
   def down
     remove_column :customers, :first_name
     remove_column :customers, :last_name
   end
-
-  def migrate_customer_name_data!
-    Customer.where(first_name: "", last_name: "").where.not(name: [nil, ""]).find_each do |customer|
-      name_words = customer.name.split(' ')
-      next if name_words.empty?
-
-      customer.update(
-        first_name: name_words.first,
-        last_name: name_words[1..].join(' ')
-      )
-    end
-  end
 end

db/migrate/20220105085730_migrate_customers_data.rb

@@ -0,0 +1,24 @@
+# frozen_string_literal: true
+
+class MigrateCustomersData < ActiveRecord::Migration[6.1]
+  class SpreeAddress < ApplicationRecord; end
+  class Customer < ApplicationRecord
+    belongs_to :bill_address, class_name: "SpreeAddress"
+  end
+
+  def up
+    migrate_customer_name_data!
+  end
+
+  def migrate_customer_name_data!
+    Customer.where(first_name: "", last_name: "").where.not(name: [nil, ""]).find_each do |customer|
+      name_words = customer.name.split(' ')
+      next if name_words.empty?
+
+      customer.update(
+        first_name: name_words.first,
+        last_name: name_words[1..].join(' ')
+      )
+    end
+  end
+end