Demonstration of working client/server

package com.j256;

import static org.junit.Assert.assertEquals;

import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.net.InetAddress;
import java.net.ServerSocket;
import java.net.Socket;

import org.junit.Test;

public class Foo {

    private static String INPUT_STRING = "Test";
    private static int PORT_NUMBER = 8000;

    @Test
    public void test() throws Exception {
        Thread server = new Thread(new Server());
        server.start();
        Thread.sleep(100);

        Thread client = new Thread(new Client());
        client.start();
        Thread.sleep(100);

        server.join();
        client.join();
    }

    private static class Server implements Runnable {
        @Override
        public void run() {
            try {
                ServerSocket serverSocket = new ServerSocket(PORT_NUMBER);
                Socket socket = serverSocket.accept();

                DataInputStream dis = new DataInputStream(socket.getInputStream());
                int arrLength = dis.readInt();

                byte[] fromClient = new byte[arrLength];
                dis.read(fromClient, 0, fromClient.length);
                assertEquals(INPUT_STRING, new String(fromClient));
                serverSocket.close();
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    }

    private static class Client implements Runnable {
        @Override
        public void run() {
            try {
                Socket socket = new Socket(InetAddress.getLocalHost(), PORT_NUMBER);
                DataOutputStream dos = new DataOutputStream(socket.getOutputStream());

                byte[] toServer = INPUT_STRING.getBytes();
                dos.writeInt(toServer.length);
                dos.write(toServer);
                socket.close();
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    }
}