alidTerminalMode(t *testing.T) {  server := newServer(t)  defer server.Shutdown()  conn := server.Dial(clientConfig())  defer conn.Close()   session, err := conn.NewSession()  if err != nil {   t.Fatalf("session failed: %v", err)  }  defer session.Close()   stdout, err := session.StdoutPipe()  if err != nil {   t.Fatalf("unable to acquire stdout pipe: %s", err)  }   stdin, err := session.StdinPipe()  if err != nil {   t.Fatalf("unable to acquire stdin pipe: %s", err)  }   tm := ssh.TerminalModes{ssh.ECHO: 0}  if err = session.RequestPty("xterm", 00, 00, tm); err != nil {   t.Fatalf("req-pty failed: %s", err)  }   err = session.Shell()  if err != nil {   t.Fatalf("session failed: %s", err)  }   stdin.Write([]byte("stty 