test: add tests for Server model

spec/factories/domain_factory.rb

@@ -42,6 +42,17 @@ FactoryBot.define do
     sequence(:name) { |n| "example#{n}.com" }
     verification_method { "DNS" }
     verified_at { Time.now }
+
+    trait :unverified do
+      verified_at { nil }
+    end
+
+    trait :dns_all_ok do
+      spf_status { "OK" }
+      dkim_status { "OK" }
+      mx_status { "OK" }
+      return_path_status { "OK" }
+    end
   end
 
   factory :organization_domain, parent: :domain do