if err != nil {
				t.Error(err)
				continue
			}
			switch addr := c.LocalAddr().(*TCPAddr); {
			case addr.IP.To4() != nil:
				dss.teardownNetwork("tcp4")
			case addr.IP.To16() != nil && addr.IP.To4() == nil:
				dss.teardownNetwork("tcp6")
			}
			c.Close()
		}
	}
}

func TestDialerKeepAlive(t *testing.T) {
	t.Cleanup(func() {
		testHookSetKeepAlive = func(KeepAliveConfig) {}

	for i := range dss.lns {
		go func(i int) {
			handler(dss, dss.lns[i].Listener)
			close(dss.lns[i].done)
		}(i)
	}
	return nil
}

func (dss *dualStackServer) teardownNetwork(network string) error {
	dss.lnmu.Lock()
	for i := range dss.lns {
		if network == dss.lns[i].network && dss.lns[i].Listener != nil {
			dss.lns[i].Listener.Close()
			<-dss.lns[i].done