t.Logf("skipping %s test", tt.network+" "+tt.address)
			continue
		}

		ln1, err := Listen(tt.network, JoinHostPort(tt.address, "0"))
		if err != nil {
			t.Fatal(err)
		}
		if err := checkFirstListener(tt.network, ln1); err != nil {
			ln1.Close()
			t.Fatal(err)
		}
		ln2, err := Listen(tt.network, JoinHostPort(tt.address, ln1.(*TCPListener).port()))
		if err == nil {
			ln2.Close()
		}