对具有由工厂方法创建的多个依赖项实例的类进行单元测试？

Question

Consider the following situation:

NOTE: Code below is only for asking the question about unit tests. Please ignore how threads are (not) handled and other problems with the code that are not question related.

I have a class that listens for a TCP connection on 2 different ports: 1234 and 5678 (could be more.. I'm using two just to keep the example small). This is done by using 2 sockets created with an abstract factory.
As soon as a client connects to one of the two ports, the class will save the socket for that TCP connection and invoke an event indicating to which port a client has connected.
The user of this class will then be able to send data using that connection.

public class ClassToTest
{
    private readonly ISocketFactory _socketFactory;

    private ISocket _connectedSocket;

    public event EventHandler<int> Connected;

    public ClassToTest(ISocketFactory socketFactory)
    {
        _socketFactory = socketFactory;
    }

    public void Listen(IPAddress ipAddress)
    {
        var listener1234 = _socketFactory.CreateTcp();
        listener1234.Bind(new IPEndPoint(ipAddress, 1234));
        listener1234.Listen(1);

        var listener5678 = _socketFactory.CreateTcp();
        listener5678.Bind(new IPEndPoint(ipAddress, 5678));
        listener5678.Listen(1);

        var thread1 = new Thread(() => 
        {
            _connectedSocket = listener1234.Accept();
            Connected?.Invoke(this, 1234);
        });

        var thread2 = new Thread(() => 
        {
            _connectedSocket = listener5678.Accept();
            Connected?.Invoke(this, 5678);
        });
    }

    public void Send(byte[] data)
    {
        _connectedSocket?.Send(data);
    }

}

Now let's say that in the unit test for this class, I inject a MockSocketFactory implementation that will return MockSockets. This way I can mock the behaviour of the sockets without relaying on real IO.

My question is: How can I distinguish in the unit test setup which of the MockSocket returned by the MockSocketFactory will be used for port 1234 and for port 5678? This without relaying on the order of calls to SocketFactory.CreateTcp() in the tested class implementation.

My idea is for example to be able to mock that the socket that is listening on port 1234 accepts a connection.

Answer 1

If you don't want to rely on the ordering of calls you should modify or overload your CreateTcp() method to take an IPEndPoint . Within the IPEndPoint , you specify the target point. This way you will determine which MockSocket is used to listen on which port.