Simulate socket in PHP unit test: socket_accept blocks

I have found this very nice suggestion to simulate a socket in PHP unit tests by creating a Socket stub: How do I unit test socket code with PHPUnit?

However, it is not clear to me how I should use this class. If I instantiate it:

$stub = new ListeningServerStub();
$stub->listen();

nothing will happen afterwards, because socket_accept blocks until it receives data. I thought about running listen() in a separate thread, but then multi-threading is not so easy in PHP. So what is a simple solution here?