How to write tests for client-server connection (sockets)?

Question

Java

Good afternoon! I am writing a client-server application. I try to cover all code with unit tests. The only thing that cannot be automated so far is the simultaneous launch of the server and the client with the exchange of some data. You have to manually start the server and client each time and manually enter data in the client, which is very tiring. Here is a rough sketch of how I thought to implement it:

import org.junit.Assert;
import org.junit.BeforeClass;
import org.junit.Test;

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

public class ServerTest {

    @BeforeClass
    public static void startServer() {
        ServerSocket listener = null;
        try {
            listener = new ServerSocket(5050);
            while (true) {
                try {
                    Socket socket = listener.accept();
                    System.out.println("Client connected");

                    DataInputStream dis = new DataInputStream(socket.getInputStream());
                    DataOutputStream dos = new DataOutputStream(socket.getOutputStream());

                    try {
                        String request = dis.readUTF();
                        System.out.println(request);
                        dos.writeUTF(request);
                    } catch (IOException e) {
                        e.printStackTrace();
                    }
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    @Test
    public void checkServerResponse() {
        try {
            Socket socket = new Socket("127.0.0.1", 5050);

            DataOutputStream dos = new DataOutputStream(socket.getOutputStream());
            DataInputStream dis = new DataInputStream(socket.getInputStream());

            String request = "Hello";
            dos.writeUTF(request);
            String serverResponse = dis.readUTF();

            Assert.assertEquals("Hello", serverResponse);

            socket.close();

        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

But this option does not work, because on the line Socket socket = listener.accept(); the test hangs. There is an idea to run the server and the client in different threads and somehow regulate them using a semaphore, but I still don’t really understand how to implement this.

Are there any generally accepted approaches to solving such problems?

Answer 1

You need to test the logic, not the work of standard classes.