move utility class below tests

Author: kyra-rk

tests/MongoDB.Bson.Tests/Serialization/BsonSerializerRegistryTests.cs

@@ -145,20 +145,6 @@ public void TryRegisterSerializer_should_allow_serializer_for_base_type()
             subject.GetSerializer(typeof(List<Person>)).Should().BeSameAs(serializer);
         }
 
-        private class Person
-        {
-            public string Name { get; set; }
-        }
-
-        private class PeopleSerializer : SerializerBase<IEnumerable<Person>>
-        {
-            public override void Serialize(BsonSerializationContext context, BsonSerializationArgs args, IEnumerable<Person> value)
-                => throw new NotImplementedException();
-
-            public override IEnumerable<Person> Deserialize(BsonDeserializationContext context, BsonDeserializationArgs args)
-                => throw new NotImplementedException();
-        }
-
         [Fact]
         public void TryRegisterSerializer_should_return_true_when_serializer_is_not_already_registered()
         {
@@ -251,5 +237,19 @@ public void TryRegisterSerializer_should_throw_when_different_serializer_is_alre
             exception.Should().BeOfType<BsonSerializationException>();
             exception.Message.Should().Contain("There is already a different serializer registered for type Object");
         }
+
+        private class Person
+        {
+            public string Name { get; set; }
+        }
+
+        private class PeopleSerializer : SerializerBase<IEnumerable<Person>>
+        {
+            public override void Serialize(BsonSerializationContext context, BsonSerializationArgs args, IEnumerable<Person> value)
+                => throw new NotImplementedException();
+
+            public override IEnumerable<Person> Deserialize(BsonDeserializationContext context, BsonDeserializationArgs args)
+                => throw new NotImplementedException();
+        }
     }
 }