TDD and Mocking out TcpClient

Question

How do people approach mocking out TcpClient (or things like TcpClient)?

I have a service that takes in a TcpClient. Should I wrap that in something else more mockable? How should I approach this?

Answer 1

When coming to mock classes that are not test friendly (i.e. sealed/not implementing any interface/methods are not virtual), you would probably want to use the Adapter design pattern.

In this pattern you add a wrapping class that implements an interface. You should then mock the interface, and make sure all your code uses that interface instead of the unfriendly concrete class. It would look something like this:

public interface ITcpClient
{
   Stream GetStream(); 
   // Anything you need here       
}
public class TcpClientAdapter: ITcpClient
{
   private TcpClient wrappedClient;
   public TcpClientAdapter(TcpClient client)
   {
    wrappedClient = client;
   }

   public Stream GetStream()
   {
     return wrappedClient.GetStream();
   }
}