Java套接字连接关闭而不调用关闭连接

我有一个服务器和客户端套接字应用程序，如下所示

   public class ServerApp { 

        public void start(int port) throws IOException {
                serverSocket = new ServerSocket(port);
                clientSocket = serverSocket.accept();
                out = new PrintWriter(clientSocket.getOutputStream(), true);
                in = new BufferedReader(new InputStreamReader(clientSocket.getInputStream()));
                String instr = in.readLine();
                //do somethings
                out.println("done")
        }

        public static void main(String[] args) throws IOException {
                ServerApp server = new ServerApp();
                server.start(6666);
        }
      }

public class ClientApp {

    public void startConnection(String ip, int port) throws UnknownHostException, IOException {
        clientSocket = new Socket(ip, port);
        out = new PrintWriter(clientSocket.getOutputStream(), true);
        in = new BufferedReader(new InputStreamReader(clientSocket.getInputStream()));
    }

    public String sendMessage(String msg) throws IOException {
        out.println(msg);
        String resp = in.readLine();
        return resp;
    }
}

单元测试类

public class UnitTest {
    @Test
    public void testSend() throws UnknownHostException, IOException {
        ClientApp client = new ClientApp();
        client.startConnection("127.0.0.1", 6666);
        String response = client.sendMessage("test msg");
        assertEquals("done", response);
    }
}

问题是，即使我执行一次单元测试，服务器连接也会断开。我没有明确指定要关闭的套接字

我还想在我的测试用例中添加以下内容，但由于服务器连接断开，只有第一次执行成功，第二次执行失败

---

@测试（invocationCount=5，threadPoolSize=3）

您的服务器只接受一个连接。在响应第一个客户端之后，它停止接收连接。为了持续连接到服务器，您需要将accept例程放入一个循环中

Define'getdisconnect'。这里没有任何东西可以检测到这一点。