Added unit tests for introduced unit test configuration setting builders.

src/Umbraco.Core/Configuration/Models/SmtpSettings.cs

@@ -1,4 +1,5 @@
-using System.ComponentModel.DataAnnotations;
+using System;
+using System.ComponentModel.DataAnnotations;
 using System.Net.Mail;
 using Umbraco.Core.Configuration.Models.Validation;
 
@@ -16,7 +17,18 @@ namespace Umbraco.Core.Configuration.Models
 
         public string PickupDirectoryLocation { get; set; }
 
-        public SmtpDeliveryMethod DeliveryMethod { get; set; }
+        // See notes on ContentSettings.MacroErrors
+        internal string DeliveryMethod { get; set; }
+
+        public SmtpDeliveryMethod DeliveryMethodValue
+        {
+            get
+            {
+                return Enum.TryParse<SmtpDeliveryMethod>(DeliveryMethod, true, out var value)
+                    ? value
+                    : SmtpDeliveryMethod.Network;
+            }
+        }
 
         public string Username { get; set; }
 

src/Umbraco.Core/Configuration/Models/Validation/GlobalSettingsValidator.cs

@@ -1,4 +1,5 @@
-using Microsoft.Extensions.Options;
+using System.Net.Mail;
+using Microsoft.Extensions.Options;
 
 namespace Umbraco.Core.Configuration.Models.Validation
 {
@@ -17,7 +18,8 @@ namespace Umbraco.Core.Configuration.Models.Validation
 
         private bool ValidateSmtpSetting(SmtpSettings value, out string message)
         {
-            return ValidateOptionalEntry("Global:Smtp", value, "A valid From email address is required", out message);
+            return ValidateOptionalEntry("Global:Smtp", value, "A valid From email address is required", out message) &&
+                ValidateStringIsOneOfEnumValues("Global:Smtp:DeliveryMethod", value.DeliveryMethod, typeof(SmtpDeliveryMethod), out message);
         }
     }
 }