test: add tests for Server model

spec/factories/ip_pool_rule_factory.rb

@@ -0,0 +1,15 @@
+# frozen_string_literal: true
+
+FactoryBot.define do
+  factory :ip_pool_rule do
+    owner factory: :organization
+    ip_pool
+    to_text { "google.com" }
+
+    after(:build) do |ip_pool_rule|
+      if ip_pool_rule.ip_pool.organizations.empty? && ip_pool_rule.owner.is_a?(Organization)
+        ip_pool_rule.ip_pool.organizations << ip_pool_rule.owner
+      end
+    end
+  end
+end