Say I want to mock out a framework class which doesn't implement an interface

Program.cs

using System;

public class ExchangeService
{
    public void Subscribe()
    {
        Console.WriteLine("Exchange: Subscribe");
    }

    public void Unsubscribe()
    {
        Console.WriteLine("Exchange: Unsubscribe");
    }
}

class SubscriptionHandlerA
{
    private readonly ExchangeService _service;
    public SubscriptionHandlerA(ExchangeService service)
    {
        _service = service;
    }

    public void Subscribe()
    {
        // do something more
        _service.Subscribe();
        // do something more
    }

    public void Unsubscribe()
    {
        // do something more
        _service.Unsubscribe();
        // do something more
    }
}

public interface IExchangeServiceAdapter
{
    void Subscribe();
    void Unsubscribe();
}

public class ExchangeServiceAdapter: IExchangeServiceAdapter
{
    private readonly ExchangeService _service;

    public ExchangeServiceAdapter(ExchangeService service)
    {
        _service = service;
    }

    public void Subscribe()
    {
        _service.Subscribe();
    }

    public void Unsubscribe()
    {
        _service.Unsubscribe();
    }

}

public class ExchangeServiceMock: IExchangeServiceAdapter
{
    public void Subscribe()
    {
        Console.WriteLine("ExchangeServiceMock: Subscribe");
    }

    public void Unsubscribe()
    {
        Console.WriteLine("ExchangeServiceMock: Unsubscribe");
    }
}

class SubscriptionHandlerB
{
    private readonly IExchangeServiceAdapter _service;
    public SubscriptionHandlerB(IExchangeServiceAdapter service)
    {
        _service = service;
    }

    public void Subscribe()
    {
        _service.Subscribe();
    }

    public void Unsubscribe()
    {
        _service.Unsubscribe();
    }
}


class Program
{
    static void Main(string[] args)
    {
        var handlerA = new SubscriptionHandlerA(new ExchangeService());
        handlerA.Subscribe();
        handlerA.Unsubscribe();

        var handlerB = new SubscriptionHandlerB(
            new ExchangeServiceAdapter(
                new ExchangeService()));
        handlerB.Subscribe();
        handlerB.Unsubscribe();

        var handlerBWithMock = new SubscriptionHandlerB(new ExchangeServiceMock());
        handlerBWithMock.Subscribe();
        handlerBWithMock.Unsubscribe();
    }
}

I like the following part:

"Say I want to mock out a framework class which doesn't implement an interface (and doesn't have virtual methods). With many mocking apis this is hard or impossible to do. What I will do, then, is define my own interface as a subset of the signature of the class I'm targeting."

from https://stackoverflow.com/questions/1299167/understanding-adapter-pattern

Also I like the following:

• https://social.msdn.microsoft.com/Forums/exchange/en-US/58cc9a22-60eb-4d8b-aebc-50a76eeea632/unit-testing-with-ews-managed-api?referrer=http://social.msdn.microsoft.com/Forums/exchange/en-US/58cc9a22-60eb-4d8b-aebc-50a76eeea632/unit-testing-with-ews-managed-api?forum=exchangesvrdevelopment