testHookLookupIP = lookupLocalhost
	handler := func(dss *dualStackServer, ln Listener) {
		for {
			c, err := ln.Accept()
			if err != nil {
				return
			}
			c.Close()
		}
	}
	dss, err := newDualStackServer()
	if err != nil {
		t.Fatal(err)
	}
	if err := dss.buildup(handler); err != nil {
		dss.teardown()
		t.Fatal(err)
	}

	const N = 10
	var wg sync.WaitGroup
	wg.Add(N)

		}
	}
	dss.lns = dss.lns[:0]
	dss.lnmu.Unlock()
	dss.cmu.Lock()
	for _, c := range dss.cs {
		c.Close()
	}
	dss.cs = dss.cs[:0]
	dss.cmu.Unlock()
	return nil
}

func newDualStackServer() (*dualStackServer, error) {
	lns, err := newDualStackListener()
	if err != nil {
		return nil, err
	}
	_, port, err := SplitHostPort(lns[0].Addr().String())
	if err != nil {
		lns[0].Close()