How to test an objects Unity serializability?

I am trying to write a test harness to test an custom class''s Serializability with the Unity Serializer. My current solution is to make it a field on a parent ScriptableObject, serialize that ScriptableObject, and then attempt to read it back as a property off the SerializedObject.

Its all working except the last part, when I try to read it back I get null. I've examined the property and it seems to have null fro its object value, but says it has chidren (which I've been unable to drill down into)>

Here are the classes:

Class being tested:

     using UnityEngine;
     using System.Collections;
     
     [System.Serializable]
     public class SerializableTypeReference : UnityEngine.Object{
         [SerializeField]
         private string _name;
        
         private System.Type _type=null;
     
         public SerializableTypeReference()
         {
     
         }
     
         public SerializableTypeReference(System.Type t)
         {
             _name = t.AssemblyQualifiedName;
             _type = t;
         }
     
         public SerializableTypeReference(string name)
         {
             _name = name;
             _type = null;
         }
     
         public System.Type Type
         {
             get
             {
                 if (_type == null)
                 {
                     _type = System.Type.GetType(_name);
                 }
                 return _type;
             }
            
         }
     
     }

ScriptableObject wrapper:

 using UnityEngine;
     using System.Collections;
     
     public class SerializationTestClass : ScriptableObject
     {
         
         public SerializableTypeReference stype;
     
     }
     

Test Code:

 using UnityEngine;
 using UnityEditor;
 using NUnit.Framework;
 
 [TestFixture]
 public class SerializableTypesTest {
     
     [Test]
     public void TypeReferenceTest()
     {
         Assert.DoesNotThrow(delegate ()
         {
             System.Type t = typeof(SerializableTypesTest);
             Assert.IsNotNull(t);
             SerializationTestClass test = ScriptableObject.CreateInstance<SerializationTestClass>();
             Assert.IsNotNull(test);
             test.stype = new SerializableTypeReference(t);
             Assert.IsNotNull(test.stype);
             SerializedObject ser = (SerializedObject)new SerializedObject(test);
             Assert.IsNotNull(ser);
             SerializedProperty prop = ser.FindProperty("stype");
             Assert.IsNotNull(prop);
             SerializableTypeReference test2 = prop.objectReferenceValue as SerializableTypeReference;
             Assert.IsNotNull(test2);
             Assert.IsTrue(t == test2.Type);
         });
         
     }
 }
 

Exception in test:

 TypeReferenceTest [0.013s]
 ---
 Expected: No Exception to be thrown
   But was:   (  Expected: not null
   But was:  null
 )
   at NUnit.Framework.Assert.That (System.Object actual, IResolveConstraint expression, System.String message, System.Object[] args) [0x00000] in <filename unknown>:0 
   at NUnit.Framework.Assert.IsNotNull (System.Object anObject) [0x00000] in <filename unknown>:0 
   at SerializableTypesTest.<TypeReferenceTest>m__2 () [0x00060] in C:\Users\jeffp\Plastic\UA\GGVRExp\Assets\Scripts\Utilities\Types\UnitySerializable\Editor\SerializableTypesTest.cs:24 
   at NUnit.Framework.Constraints.VoidInvocationDescriptor.Invoke () [0x00000] in <filename unknown>:0 
   at NUnit.Framework.Constraints.ExceptionInterceptor.Intercept (System.Object invocation) [0x00000] in <filename unknown>:0
 ---
 at SerializableTypesTest.TypeReferenceTest () [0x00000] in C:\Users\jeffp\Plastic\UA\GGVRExp\Assets\Scripts\Utilities\Types\UnitySerializable\Editor\SerializableTypesTest.cs:11