defer l.Close()

	l2, _, err := CreateListener("tcp", fmt.Sprintf("127.0.0.1:%d", port), c)
	if err != nil {
		t.Fatalf("failed to create 2nd listener: %v", err)
	}
	defer l2.Close()
}

func TestCreateListenerPreventUpgrades(t *testing.T) {
	l, port, err := CreateListener("tcp", "127.0.0.1:0", net.ListenConfig{})
	if err != nil {
		t.Fatalf("failed to create listener: %v", err)
	}
	defer l.Close()