improve test setup with factory bot

spec/factories/admin_users.rb

@@ -0,0 +1,26 @@
+# frozen_string_literal: true
+
+# == Schema Information
+#
+# Table name: admin_users
+#
+#  id                     :bigint           not null, primary key
+#  email                  :string           default(""), not null
+#  encrypted_password     :string           default(""), not null
+#  remember_created_at    :datetime
+#  reset_password_sent_at :datetime
+#  reset_password_token   :string
+#  created_at             :datetime         not null
+#  updated_at             :datetime         not null
+#
+# Indexes
+#
+#  index_admin_users_on_email                 (email) UNIQUE
+#  index_admin_users_on_reset_password_token  (reset_password_token) UNIQUE
+#
+FactoryBot.define do
+  factory :admin_user do
+    sequence(:email) { |n| "admin-#{n}@example.com" }
+    password { "password" }
+  end
+end