Blog-ExtendedCustomExceptionTests.md

using System;
using System.IO;
using System.Runtime.Serialization.Formatters.Binary;
using NUnit.Framework;

// ...

[TestFixture]
public class EntityNotFoundExceptionTests
{
    private const string Message = "some message";
    private const int EntityId = 1;

    [Test]
    public void WhenNoArgs_ThenSetMessageToDefault()
    {
        var sut = new EntityNotFoundException();

        Assert.That(sut.Message, Is.EqualTo("Entity does not exist."));
    }

    [Test]
    public void WhenMessageSpecified_ThenSetMessage()
    {
        var sut = new EntityNotFoundException(Message);

        Assert.That(sut.Message, Is.EqualTo(Message));
    }

    [Test]
    public void WhenMessageAndInnerExSpecified_ThenSetMessageAndInnerEx()
    {
        var innerException = new Exception();

        var sut = new EntityNotFoundException(Message, innerException);

        Assert.That(sut.Message, Is.EqualTo(Message));
        Assert.That(sut.InnerException, Is.SameAs(innerException));
    }

    [Test]
    public void WhenIdSpecified_ThenSetProperty()
    {
        var sut = new EntityNotFoundException(EntityId);

        Assert.That(sut.Message, Is.EqualTo($"Entity does not exist with ID: '{EntityId}'."));
        Assert.That(sut.EntityId, Is.EqualTo(EntityId));
    }

    [Test]
    public void WhenSerialized_ThenDeserializeCorrectly()
    {
        var sut = new EntityNotFoundException(EntityId);

        var result = Serializer.SerializeAndDeserialize(sut);

        Assert.That(result.EntityId, Is.EqualTo(sut.EntityId));
        Assert.That(result.ToString(), Is.EqualTo(sut.ToString()));
    }
}

// ...

internal static class Serializer
{
    public static TException SerializeAndDeserialize<TException>(TException exception)
    {
        var formatter = new BinaryFormatter();
        
        using (var stream = new MemoryStream())
        {
            formatter.Serialize(stream, exception);

            stream.Seek(0, 0);

            return (TException)formatter.Deserialize(stream);
        }
    }
}