using System;

using System.Collections;

using System.Collections.Generic;

using System.Linq;

using System.Text;

using System.Runtime.Serialization.Formatters;

using System.IO;

using System.Data;

using System.ComponentModel.DataAnnotations;

using System.Globalization;

using System.Reflection;

​

using Newtonsoft.Json;

using Newtonsoft.Json.Linq;

using Newtonsoft.Json.Converters;

using Newtonsoft.Json.Serialization;    

​

using NUnit.Framework; // Throws NUnit.Framework.AssertionException

using NUnit; 

​

//https://stackoverflow.com/questions/53176481/how-to-unit-test-a-custom-jsonconverter?noredirect=1#comment93243119_53176481

​

    public class SomeObject

    {

        // Fixed renamed from destination

        public Destination Destination { get; set; }

    }

​

    public class Destination

    {

        public Destination(int destinationId)

        {

            Id = destinationId;

        }

​

        public int Id { get; set; }

    }

​

    public class DestinationConverter : JsonConverter

    {

        public override bool CanConvert(System.Type objectType)

        {

            return objectType == typeof(Destination);

        }

​

        public override object ReadJson(Newtonsoft.Json.JsonReader reader, System.Type objectType, object existingValue, Newtonsoft.Json.JsonSerializer serializer)

        {

            var id = serializer.Deserialize<int?>(reader);

            if (id == null)

                return null;

            return new Destination(id.Value);

        }

​

        public override void WriteJson(Newtonsoft.Json.JsonWriter writer, object value, Newtonsoft.Json.JsonSerializer serializer)

        {

            // WriteJson() is never called with a null value, instead Json.NET writes null automatically.

            writer.WriteValue(((Destination)value).Id);

        }

    }

​

    class TestClass

    {

        public static void Test()

        {

            new TestClass().ReadJson_can_deserialize_an_integer_as_Destination(new DestinationConverter(), 101);

        }   

​

        [Test /*, AutoData */]

        public void SomeObject_is_correctly_deserialized(SomeObject testObject)

        {

            //var json = $@"{{""destinationId"":{testObject.Destination.Id}}}";

            var json = string.Format("{{\"destinationId\":{0}}}", testObject.Destination.Id);

​

            Console.WriteLine("json: {}", json);

​

            var obj = JsonConvert.DeserializeObject<SomeObject>(json);

​

            Assert.That(obj.Destination.Id, Is.EqualTo(testObject.Destination.Id));

        }

​

        [Test /*, AutoData */]

        public void ReadJson_can_deserialize_an_integer_as_Destination(DestinationConverter sut, int testValue)

        {

            var json = string.Format("{0}", testValue);

            Console.WriteLine(json);

            JsonReader reader = new JsonTextReader(new StringReader(json));

            while (reader.TokenType == JsonToken.None)

                if (!reader.Read())

                    break;

            //Console.WriteLine(reader.TokenType);

​

            var obj = sut.ReadJson(reader, typeof(Destination), null, JsonSerializer.CreateDefault());

​

            var result = obj as Destination;

​

            obj.Dump();

            Assert.That(result, Is.Not.Null);

            Assert.That(result, Is.InstanceOf<Destination>());

            Assert.That(result.Id, Is.EqualTo(testValue));

        }

​

    }

​

    public class Program

    {

        public static void Main()

        {

            Console.WriteLine("Environment version: " + Environment.Version);

            Console.WriteLine("Json.NET version: " + typeof(JsonSerializer).Assembly.FullName);

            Console.WriteLine();

​

            try

            {

                TestClass.Test();

            }

            catch (Exception ex)

            {

                Console.WriteLine("Failed with unhandled exception: ");

                Console.WriteLine(ex);

                throw;

            }

        }

    }

​