How to simulate connect timeout error and test it

ConnectTimeoutTest.java

import java.net.HttpURLConnection;
import java.net.ServerSocket;
import java.net.Socket;
import java.net.SocketTimeoutException;
import java.net.URL;

import org.testng.Assert;
import org.testng.annotations.AfterClass;
import org.testng.annotations.BeforeClass;
import org.testng.annotations.Test;

public class ConnectTimeoutTest {

 private ServerSocket serverSocket;

 private int port;

 @BeforeClass
 public void beforeClass() throws IOException {
  //server socket with single element backlog queue (1) and dynamicaly allocated port (0)
  serverSocket = new ServerSocket(0, 1);
  //just get the allocated port
  port = serverSocket.getLocalPort();
  //fill backlog queue by this request so consequent requests will be blocked
  new Socket().connect(serverSocket.getLocalSocketAddress());
 }

 @AfterClass
 public void afterClass() throws IOException {
  //some cleanup
  if (serverSocket != null && !serverSocket.isClosed()) {
   serverSocket.close();
  }
 }

 @Test
 public void testConnect() throws IOException {
  URL url = new URL("http://localhost:" + port); //use allocated port
  HttpURLConnection connection = (HttpURLConnection) url.openConnection();
  connection.setConnectTimeout(1000);
  //connection.setReadTimeout(2000); //irelevant in this case
  try {
   connection.getInputStream();
  } catch (SocketTimeoutException stx) {
   Assert.assertEquals(stx.getMessage(), "connect timed out"); //that's what are we waiting for
  }
 }
}

At present, I'm getting:

java.net.ConnectException: Connection refused: connect

instead. I've found this answer that doesn't require a live service to test the client:

        // Connect to a non-routable IP address, such as 10.255.255.1
        URL url = new URL("http://10.255.255.1/");
        URLConnection client = url.openConnection();
        client.setConnectTimeout(100);
        SocketTimeoutException exception =
                assertThrows(SocketTimeoutException.class, () -> client.connect());
        assertEquals("exception message", exception.getMessage(), "connect timed out");