diff --git a/icmp/diag_test.go b/icmp/diag_test.go
index d2c13422..8437690e 100644
--- a/icmp/diag_test.go
+++ b/icmp/diag_test.go
@@ -17,9 +17,9 @@ import (
 
 	"golang.org/x/net/icmp"
 	"golang.org/x/net/internal/iana"
-	"golang.org/x/net/internal/nettest"
 	"golang.org/x/net/ipv4"
 	"golang.org/x/net/ipv6"
+	"golang.org/x/net/nettest"
 )
 
 var testDiag = flag.Bool("diag", false, "whether to test ICMP message exchange with external network")
@@ -68,8 +68,8 @@ func TestDiag(t *testing.T) {
 		}
 	})
 	t.Run("Ping/Privileged", func(t *testing.T) {
-		if m, ok := nettest.SupportsRawIPSocket(); !ok {
-			t.Skip(m)
+		if !nettest.SupportsRawSocket() {
+			t.Skipf("not supported on %s/%s", runtime.GOOS, runtime.GOARCH)
 		}
 		for i, dt := range []diagTest{
 			{
@@ -100,8 +100,8 @@ func TestDiag(t *testing.T) {
 		}
 	})
 	t.Run("Probe/Privileged", func(t *testing.T) {
-		if m, ok := nettest.SupportsRawIPSocket(); !ok {
-			t.Skip(m)
+		if !nettest.SupportsRawSocket() {
+			t.Skipf("not supported on %s/%s", runtime.GOOS, runtime.GOARCH)
 		}
 		for i, dt := range []diagTest{
 			{
diff --git a/internal/nettest/helper_nobsd.go b/internal/nettest/helper_nobsd.go
deleted file mode 100644
index bfcaee97..00000000
--- a/internal/nettest/helper_nobsd.go
+++ /dev/null
@@ -1,11 +0,0 @@
-// Copyright 2016 The Go Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style
-// license that can be found in the LICENSE file.
-
-// +build aix linux solaris
-
-package nettest
-
-func supportsIPv6MulticastDeliveryOnLoopback() bool {
-	return true
-}
diff --git a/internal/nettest/helper_stub.go b/internal/nettest/helper_stub.go
deleted file mode 100644
index 2eeeb353..00000000
--- a/internal/nettest/helper_stub.go
+++ /dev/null
@@ -1,28 +0,0 @@
-// Copyright 2014 The Go Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style
-// license that can be found in the LICENSE file.
-
-// +build js nacl plan9
-
-package nettest
-
-import (
-	"fmt"
-	"runtime"
-)
-
-func maxOpenFiles() int {
-	return defaultMaxOpenFiles
-}
-
-func supportsRawIPSocket() (string, bool) {
-	return fmt.Sprintf("not supported on %s", runtime.GOOS), false
-}
-
-func supportsIPv6MulticastDeliveryOnLoopback() bool {
-	return false
-}
-
-func protocolNotSupported(err error) bool {
-	return false
-}
diff --git a/internal/nettest/helper_windows.go b/internal/nettest/helper_windows.go
deleted file mode 100644
index b0a6a30c..00000000
--- a/internal/nettest/helper_windows.go
+++ /dev/null
@@ -1,38 +0,0 @@
-// Copyright 2015 The Go Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style
-// license that can be found in the LICENSE file.
-
-package nettest
-
-import (
-	"fmt"
-	"runtime"
-	"syscall"
-)
-
-func maxOpenFiles() int {
-	return 4 * defaultMaxOpenFiles /* actually it's 16581375 */
-}
-
-func supportsRawIPSocket() (string, bool) {
-	// From http://msdn.microsoft.com/en-us/library/windows/desktop/ms740548.aspx:
-	// Note: To use a socket of type SOCK_RAW requires administrative privileges.
-	// Users running Winsock applications that use raw sockets must be a member of
-	// the Administrators group on the local computer, otherwise raw socket calls
-	// will fail with an error code of WSAEACCES. On Windows Vista and later, access
-	// for raw sockets is enforced at socket creation. In earlier versions of Windows,
-	// access for raw sockets is enforced during other socket operations.
-	s, err := syscall.Socket(syscall.AF_INET, syscall.SOCK_RAW, 0)
-	if err == syscall.WSAEACCES {
-		return fmt.Sprintf("no access to raw socket allowed on %s", runtime.GOOS), false
-	}
-	if err != nil {
-		return err.Error(), false
-	}
-	syscall.Closesocket(s)
-	return "", true
-}
-
-func supportsIPv6MulticastDeliveryOnLoopback() bool {
-	return true
-}
diff --git a/internal/nettest/interface.go b/internal/nettest/interface.go
deleted file mode 100644
index 8e6333af..00000000
--- a/internal/nettest/interface.go
+++ /dev/null
@@ -1,94 +0,0 @@
-// Copyright 2012 The Go Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style
-// license that can be found in the LICENSE file.
-
-package nettest
-
-import "net"
-
-// IsMulticastCapable reports whether ifi is an IP multicast-capable
-// network interface. Network must be "ip", "ip4" or "ip6".
-func IsMulticastCapable(network string, ifi *net.Interface) (net.IP, bool) {
-	switch network {
-	case "ip", "ip4", "ip6":
-	default:
-		return nil, false
-	}
-	if ifi == nil || ifi.Flags&net.FlagUp == 0 || ifi.Flags&net.FlagMulticast == 0 {
-		return nil, false
-	}
-	return hasRoutableIP(network, ifi)
-}
-
-// RoutedInterface returns a network interface that can route IP
-// traffic and satisfies flags. It returns nil when an appropriate
-// network interface is not found. Network must be "ip", "ip4" or
-// "ip6".
-func RoutedInterface(network string, flags net.Flags) *net.Interface {
-	switch network {
-	case "ip", "ip4", "ip6":
-	default:
-		return nil
-	}
-	ift, err := net.Interfaces()
-	if err != nil {
-		return nil
-	}
-	for _, ifi := range ift {
-		if ifi.Flags&flags != flags {
-			continue
-		}
-		if _, ok := hasRoutableIP(network, &ifi); !ok {
-			continue
-		}
-		return &ifi
-	}
-	return nil
-}
-
-func hasRoutableIP(network string, ifi *net.Interface) (net.IP, bool) {
-	ifat, err := ifi.Addrs()
-	if err != nil {
-		return nil, false
-	}
-	for _, ifa := range ifat {
-		switch ifa := ifa.(type) {
-		case *net.IPAddr:
-			if ip := routableIP(network, ifa.IP); ip != nil {
-				return ip, true
-			}
-		case *net.IPNet:
-			if ip := routableIP(network, ifa.IP); ip != nil {
-				return ip, true
-			}
-		}
-	}
-	return nil, false
-}
-
-func routableIP(network string, ip net.IP) net.IP {
-	if !ip.IsLoopback() && !ip.IsLinkLocalUnicast() && !ip.IsGlobalUnicast() {
-		return nil
-	}
-	switch network {
-	case "ip4":
-		if ip := ip.To4(); ip != nil {
-			return ip
-		}
-	case "ip6":
-		if ip.IsLoopback() { // addressing scope of the loopback address depends on each implementation
-			return nil
-		}
-		if ip := ip.To16(); ip != nil && ip.To4() == nil {
-			return ip
-		}
-	default:
-		if ip := ip.To4(); ip != nil {
-			return ip
-		}
-		if ip := ip.To16(); ip != nil {
-			return ip
-		}
-	}
-	return nil
-}
diff --git a/internal/nettest/rlimit.go b/internal/nettest/rlimit.go
deleted file mode 100644
index bb34aec0..00000000
--- a/internal/nettest/rlimit.go
+++ /dev/null
@@ -1,11 +0,0 @@
-// Copyright 2015 The Go Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style
-// license that can be found in the LICENSE file.
-
-package nettest
-
-const defaultMaxOpenFiles = 256
-
-// MaxOpenFiles returns the maximum number of open files for the
-// caller's process.
-func MaxOpenFiles() int { return maxOpenFiles() }
diff --git a/internal/nettest/stack.go b/internal/nettest/stack.go
deleted file mode 100644
index 3b8a01e9..00000000
--- a/internal/nettest/stack.go
+++ /dev/null
@@ -1,152 +0,0 @@
-// Copyright 2014 The Go Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style
-// license that can be found in the LICENSE file.
-
-// Package nettest provides utilities for network testing.
-package nettest // import "golang.org/x/net/internal/nettest"
-
-import (
-	"fmt"
-	"io/ioutil"
-	"net"
-	"os"
-	"runtime"
-)
-
-var (
-	supportsIPv4 bool
-	supportsIPv6 bool
-)
-
-func init() {
-	if ln, err := net.Listen("tcp4", "127.0.0.1:0"); err == nil {
-		ln.Close()
-		supportsIPv4 = true
-	}
-	if ln, err := net.Listen("tcp6", "[::1]:0"); err == nil {
-		ln.Close()
-		supportsIPv6 = true
-	}
-}
-
-// SupportsIPv4 reports whether the platform supports IPv4 networking
-// functionality.
-func SupportsIPv4() bool { return supportsIPv4 }
-
-// SupportsIPv6 reports whether the platform supports IPv6 networking
-// functionality.
-func SupportsIPv6() bool { return supportsIPv6 }
-
-// SupportsRawIPSocket reports whether the platform supports raw IP
-// sockets.
-func SupportsRawIPSocket() (string, bool) {
-	return supportsRawIPSocket()
-}
-
-// SupportsIPv6MulticastDeliveryOnLoopback reports whether the
-// platform supports IPv6 multicast packet delivery on software
-// loopback interface.
-func SupportsIPv6MulticastDeliveryOnLoopback() bool {
-	return supportsIPv6MulticastDeliveryOnLoopback()
-}
-
-// ProtocolNotSupported reports whether err is a protocol not
-// supported error.
-func ProtocolNotSupported(err error) bool {
-	return protocolNotSupported(err)
-}
-
-// TestableNetwork reports whether network is testable on the current
-// platform configuration.
-func TestableNetwork(network string) bool {
-	// This is based on logic from standard library's
-	// net/platform_test.go.
-	switch network {
-	case "unix", "unixgram":
-		switch runtime.GOOS {
-		case "android", "js", "nacl", "plan9", "windows":
-			return false
-		}
-		if runtime.GOOS == "darwin" && (runtime.GOARCH == "arm" || runtime.GOARCH == "arm64") {
-			return false
-		}
-	case "unixpacket":
-		switch runtime.GOOS {
-		case "aix", "android", "darwin", "freebsd", "js", "nacl", "plan9", "windows":
-			return false
-		case "netbsd":
-			// It passes on amd64 at least. 386 fails (Issue 22927). arm is unknown.
-			if runtime.GOARCH == "386" {
-				return false
-			}
-		}
-	}
-	return true
-}
-
-// NewLocalListener returns a listener which listens to a loopback IP
-// address or local file system path.
-// Network must be "tcp", "tcp4", "tcp6", "unix" or "unixpacket".
-func NewLocalListener(network string) (net.Listener, error) {
-	switch network {
-	case "tcp":
-		if supportsIPv4 {
-			if ln, err := net.Listen("tcp4", "127.0.0.1:0"); err == nil {
-				return ln, nil
-			}
-		}
-		if supportsIPv6 {
-			return net.Listen("tcp6", "[::1]:0")
-		}
-	case "tcp4":
-		if supportsIPv4 {
-			return net.Listen("tcp4", "127.0.0.1:0")
-		}
-	case "tcp6":
-		if supportsIPv6 {
-			return net.Listen("tcp6", "[::1]:0")
-		}
-	case "unix", "unixpacket":
-		return net.Listen(network, localPath())
-	}
-	return nil, fmt.Errorf("%s is not supported", network)
-}
-
-// NewLocalPacketListener returns a packet listener which listens to a
-// loopback IP address or local file system path.
-// Network must be "udp", "udp4", "udp6" or "unixgram".
-func NewLocalPacketListener(network string) (net.PacketConn, error) {
-	switch network {
-	case "udp":
-		if supportsIPv4 {
-			if c, err := net.ListenPacket("udp4", "127.0.0.1:0"); err == nil {
-				return c, nil
-			}
-		}
-		if supportsIPv6 {
-			return net.ListenPacket("udp6", "[::1]:0")
-		}
-	case "udp4":
-		if supportsIPv4 {
-			return net.ListenPacket("udp4", "127.0.0.1:0")
-		}
-	case "udp6":
-		if supportsIPv6 {
-			return net.ListenPacket("udp6", "[::1]:0")
-		}
-	case "unixgram":
-		return net.ListenPacket(network, localPath())
-	}
-	return nil, fmt.Errorf("%s is not supported", network)
-}
-
-func localPath() string {
-	f, err := ioutil.TempFile("", "nettest")
-	if err != nil {
-		panic(err)
-	}
-	path := f.Name()
-	f.Close()
-	os.Remove(path)
-	return path
-}
diff --git a/internal/socket/socket_test.go b/internal/socket/socket_test.go
index 5de1b9fb..3d9e77eb 100644
--- a/internal/socket/socket_test.go
+++ b/internal/socket/socket_test.go
@@ -14,8 +14,8 @@ import (
 	"syscall"
 	"testing"
 
-	"golang.org/x/net/internal/nettest"
 	"golang.org/x/net/internal/socket"
+	"golang.org/x/net/nettest"
 )
 
 func TestSocket(t *testing.T) {
diff --git a/internal/sockstest/server.go b/internal/sockstest/server.go
index 3c6e9e95..dc2fa67c 100644
--- a/internal/sockstest/server.go
+++ b/internal/sockstest/server.go
@@ -10,8 +10,8 @@ import (
 	"io"
 	"net"
 
-	"golang.org/x/net/internal/nettest"
 	"golang.org/x/net/internal/socks"
+	"golang.org/x/net/nettest"
 )
 
 // An AuthRequest represents an authentication request.
diff --git a/internal/nettest/helper_posix.go b/ipv4/helper_posix_test.go
similarity index 97%
rename from internal/nettest/helper_posix.go
rename to ipv4/helper_posix_test.go
index efc67a8e..ee66dd28 100644
--- a/internal/nettest/helper_posix.go
+++ b/ipv4/helper_posix_test.go
@@ -4,7 +4,7 @@
 
 // +build aix darwin dragonfly freebsd linux netbsd openbsd solaris windows
 
-package nettest
+package ipv4_test
 
 import (
 	"os"
diff --git a/ipv4/helper_stub_test.go b/ipv4/helper_stub_test.go
new file mode 100644
index 00000000..4ba01714
--- /dev/null
+++ b/ipv4/helper_stub_test.go
@@ -0,0 +1,11 @@
+// Copyright 2014 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// +build !aix,!darwin,!dragonfly,!freebsd,!linux,!netbsd,!openbsd,!solaris,!windows
+
+package ipv4_test
+
+func protocolNotSupported(err error) bool {
+	return false
+}
diff --git a/ipv4/icmp_test.go b/ipv4/icmp_test.go
index 3324b54d..d51acce8 100644
--- a/ipv4/icmp_test.go
+++ b/ipv4/icmp_test.go
@@ -10,8 +10,8 @@ import (
 	"runtime"
 	"testing"
 
-	"golang.org/x/net/internal/nettest"
 	"golang.org/x/net/ipv4"
+	"golang.org/x/net/nettest"
 )
 
 var icmpStringTests = []struct {
@@ -66,8 +66,8 @@ func TestSetICMPFilter(t *testing.T) {
 	default:
 		t.Skipf("not supported on %s", runtime.GOOS)
 	}
-	if m, ok := nettest.SupportsRawIPSocket(); !ok {
-		t.Skip(m)
+	if !nettest.SupportsRawSocket() {
+		t.Skipf("not supported on %s/%s", runtime.GOOS, runtime.GOARCH)
 	}
 
 	c, err := net.ListenPacket("ip4:icmp", "127.0.0.1")
diff --git a/ipv4/multicast_test.go b/ipv4/multicast_test.go
index fd9efe00..7271dd0a 100644
--- a/ipv4/multicast_test.go
+++ b/ipv4/multicast_test.go
@@ -14,8 +14,8 @@ import (
 
 	"golang.org/x/net/icmp"
 	"golang.org/x/net/internal/iana"
-	"golang.org/x/net/internal/nettest"
 	"golang.org/x/net/ipv4"
+	"golang.org/x/net/nettest"
 )
 
 var packetConnReadWriteMulticastUDPTests = []struct {
@@ -32,8 +32,8 @@ func TestPacketConnReadWriteMulticastUDP(t *testing.T) {
 	case "aix", "fuchsia", "hurd", "js", "nacl", "plan9", "solaris", "windows":
 		t.Skipf("not supported on %s", runtime.GOOS)
 	}
-	ifi := nettest.RoutedInterface("ip4", net.FlagUp|net.FlagMulticast|net.FlagLoopback)
-	if ifi == nil {
+	ifi, err := nettest.RoutedInterface("ip4", net.FlagUp|net.FlagMulticast|net.FlagLoopback)
+	if err != nil {
 		t.Skipf("not available on %s", runtime.GOOS)
 	}
 
@@ -82,7 +82,7 @@ func TestPacketConnReadWriteMulticastUDP(t *testing.T) {
 
 		for i, toggle := range []bool{true, false, true} {
 			if err := p.SetControlMessage(cf, toggle); err != nil {
-				if nettest.ProtocolNotSupported(err) {
+				if protocolNotSupported(err) {
 					t.Logf("not supported on %s", runtime.GOOS)
 					continue
 				}
@@ -120,11 +120,11 @@ func TestPacketConnReadWriteMulticastICMP(t *testing.T) {
 	case "aix", "fuchsia", "hurd", "js", "nacl", "plan9", "solaris", "windows":
 		t.Skipf("not supported on %s", runtime.GOOS)
 	}
-	if m, ok := nettest.SupportsRawIPSocket(); !ok {
-		t.Skip(m)
+	if !nettest.SupportsRawSocket() {
+		t.Skipf("not supported on %s/%s", runtime.GOOS, runtime.GOARCH)
 	}
-	ifi := nettest.RoutedInterface("ip4", net.FlagUp|net.FlagMulticast|net.FlagLoopback)
-	if ifi == nil {
+	ifi, err := nettest.RoutedInterface("ip4", net.FlagUp|net.FlagMulticast|net.FlagLoopback)
+	if err != nil {
 		t.Skipf("not available on %s", runtime.GOOS)
 	}
 
@@ -184,7 +184,7 @@ func TestPacketConnReadWriteMulticastICMP(t *testing.T) {
 				t.Fatal(err)
 			}
 			if err := p.SetControlMessage(cf, toggle); err != nil {
-				if nettest.ProtocolNotSupported(err) {
+				if protocolNotSupported(err) {
 					t.Logf("not supported on %s", runtime.GOOS)
 					continue
 				}
@@ -234,11 +234,11 @@ func TestRawConnReadWriteMulticastICMP(t *testing.T) {
 	if testing.Short() {
 		t.Skip("to avoid external network")
 	}
-	if m, ok := nettest.SupportsRawIPSocket(); !ok {
-		t.Skip(m)
+	if !nettest.SupportsRawSocket() {
+		t.Skipf("not supported on %s/%s", runtime.GOOS, runtime.GOARCH)
 	}
-	ifi := nettest.RoutedInterface("ip4", net.FlagUp|net.FlagMulticast|net.FlagLoopback)
-	if ifi == nil {
+	ifi, err := nettest.RoutedInterface("ip4", net.FlagUp|net.FlagMulticast|net.FlagLoopback)
+	if err != nil {
 		t.Skipf("not available on %s", runtime.GOOS)
 	}
 
@@ -305,7 +305,7 @@ func TestRawConnReadWriteMulticastICMP(t *testing.T) {
 				Dst:      tt.grp.IP,
 			}
 			if err := r.SetControlMessage(cf, toggle); err != nil {
-				if nettest.ProtocolNotSupported(err) {
+				if protocolNotSupported(err) {
 					t.Logf("not supported on %s", runtime.GOOS)
 					continue
 				}
diff --git a/ipv4/multicastlistener_test.go b/ipv4/multicastlistener_test.go
index 73e509dd..591489e4 100644
--- a/ipv4/multicastlistener_test.go
+++ b/ipv4/multicastlistener_test.go
@@ -9,8 +9,8 @@ import (
 	"runtime"
 	"testing"
 
-	"golang.org/x/net/internal/nettest"
 	"golang.org/x/net/ipv4"
+	"golang.org/x/net/nettest"
 )
 
 var udpMultipleGroupListenerTests = []net.Addr{
@@ -43,7 +43,7 @@ func TestUDPSinglePacketConnWithMultipleGroupListeners(t *testing.T) {
 			t.Fatal(err)
 		}
 		for i, ifi := range ift {
-			if _, ok := nettest.IsMulticastCapable("ip4", &ifi); !ok {
+			if _, err := nettest.MulticastSource("ip4", &ifi); err != nil {
 				continue
 			}
 			if err := p.JoinGroup(&ifi, gaddr); err != nil {
@@ -94,7 +94,7 @@ func TestUDPMultiplePacketConnWithMultipleGroupListeners(t *testing.T) {
 			t.Fatal(err)
 		}
 		for i, ifi := range ift {
-			if _, ok := nettest.IsMulticastCapable("ip4", &ifi); !ok {
+			if _, err := nettest.MulticastSource("ip4", &ifi); err != nil {
 				continue
 			}
 			for _, p := range ps {
@@ -136,8 +136,8 @@ func TestUDPPerInterfaceSinglePacketConnWithSingleGroupListener(t *testing.T) {
 	}
 	port := "0"
 	for i, ifi := range ift {
-		ip, ok := nettest.IsMulticastCapable("ip4", &ifi)
-		if !ok {
+		ip, err := nettest.MulticastSource("ip4", &ifi)
+		if err != nil {
 			continue
 		}
 		c, err := net.ListenPacket("udp4", net.JoinHostPort(ip.String(), port)) // unicast address with non-reusable port
@@ -178,8 +178,8 @@ func TestIPSingleRawConnWithSingleGroupListener(t *testing.T) {
 	if testing.Short() {
 		t.Skip("to avoid external network")
 	}
-	if m, ok := nettest.SupportsRawIPSocket(); !ok {
-		t.Skip(m)
+	if !nettest.SupportsRawSocket() {
+		t.Skipf("not supported on %s/%s", runtime.GOOS, runtime.GOARCH)
 	}
 
 	c, err := net.ListenPacket("ip4:icmp", "0.0.0.0") // wildcard address
@@ -200,7 +200,7 @@ func TestIPSingleRawConnWithSingleGroupListener(t *testing.T) {
 		t.Fatal(err)
 	}
 	for i, ifi := range ift {
-		if _, ok := nettest.IsMulticastCapable("ip4", &ifi); !ok {
+		if _, err := nettest.MulticastSource("ip4", &ifi); err != nil {
 			continue
 		}
 		if err := r.JoinGroup(&ifi, &gaddr); err != nil {
@@ -223,8 +223,8 @@ func TestIPPerInterfaceSingleRawConnWithSingleGroupListener(t *testing.T) {
 	if testing.Short() {
 		t.Skip("to avoid external network")
 	}
-	if m, ok := nettest.SupportsRawIPSocket(); !ok {
-		t.Skip(m)
+	if !nettest.SupportsRawSocket() {
+		t.Skipf("not supported on %s/%s", runtime.GOOS, runtime.GOARCH)
 	}
 
 	gaddr := net.IPAddr{IP: net.IPv4(224, 0, 0, 254)} // see RFC 4727
@@ -239,8 +239,8 @@ func TestIPPerInterfaceSingleRawConnWithSingleGroupListener(t *testing.T) {
 		t.Fatal(err)
 	}
 	for i, ifi := range ift {
-		ip, ok := nettest.IsMulticastCapable("ip4", &ifi)
-		if !ok {
+		ip, err := nettest.MulticastSource("ip4", &ifi)
+		if err != nil {
 			continue
 		}
 		c, err := net.ListenPacket("ip4:253", ip.String()) // unicast address
diff --git a/ipv4/multicastsockopt_test.go b/ipv4/multicastsockopt_test.go
index fd783d05..e9f2c57b 100644
--- a/ipv4/multicastsockopt_test.go
+++ b/ipv4/multicastsockopt_test.go
@@ -9,8 +9,8 @@ import (
 	"runtime"
 	"testing"
 
-	"golang.org/x/net/internal/nettest"
 	"golang.org/x/net/ipv4"
+	"golang.org/x/net/nettest"
 )
 
 var packetConnMulticastSocketOptionTests = []struct {
@@ -29,15 +29,15 @@ func TestPacketConnMulticastSocketOptions(t *testing.T) {
 	case "aix", "fuchsia", "hurd", "js", "nacl", "plan9":
 		t.Skipf("not supported on %s", runtime.GOOS)
 	}
-	ifi := nettest.RoutedInterface("ip4", net.FlagUp|net.FlagMulticast|net.FlagLoopback)
-	if ifi == nil {
+	ifi, err := nettest.RoutedInterface("ip4", net.FlagUp|net.FlagMulticast|net.FlagLoopback)
+	if err != nil {
 		t.Skipf("not available on %s", runtime.GOOS)
 	}
 
-	m, ok := nettest.SupportsRawIPSocket()
+	ok := nettest.SupportsRawSocket()
 	for _, tt := range packetConnMulticastSocketOptionTests {
 		if tt.net == "ip4" && !ok {
-			t.Log(m)
+			t.Logf("not supported on %s/%s", runtime.GOOS, runtime.GOARCH)
 			continue
 		}
 		c, err := net.ListenPacket(tt.net+tt.proto, tt.addr)
@@ -69,11 +69,11 @@ func TestRawConnMulticastSocketOptions(t *testing.T) {
 	case "aix", "fuchsia", "hurd", "js", "nacl", "plan9":
 		t.Skipf("not supported on %s", runtime.GOOS)
 	}
-	if m, ok := nettest.SupportsRawIPSocket(); !ok {
-		t.Skip(m)
+	if !nettest.SupportsRawSocket() {
+		t.Skipf("not supported on %s/%s", runtime.GOOS, runtime.GOARCH)
 	}
-	ifi := nettest.RoutedInterface("ip4", net.FlagUp|net.FlagMulticast|net.FlagLoopback)
-	if ifi == nil {
+	ifi, err := nettest.RoutedInterface("ip4", net.FlagUp|net.FlagMulticast|net.FlagLoopback)
+	if err != nil {
 		t.Skipf("not available on %s", runtime.GOOS)
 	}
 
diff --git a/ipv4/readwrite_test.go b/ipv4/readwrite_test.go
index acf87d1e..5b8b9d31 100644
--- a/ipv4/readwrite_test.go
+++ b/ipv4/readwrite_test.go
@@ -14,8 +14,8 @@ import (
 	"testing"
 
 	"golang.org/x/net/internal/iana"
-	"golang.org/x/net/internal/nettest"
 	"golang.org/x/net/ipv4"
+	"golang.org/x/net/nettest"
 )
 
 func BenchmarkReadWriteUnicast(b *testing.B) {
@@ -50,7 +50,7 @@ func BenchmarkReadWriteUnicast(b *testing.B) {
 			b.Fatal(err)
 		}
 		cm := ipv4.ControlMessage{TTL: 1}
-		ifi := nettest.RoutedInterface("ip4", net.FlagUp|net.FlagLoopback)
+		ifi, _ := nettest.RoutedInterface("ip4", net.FlagUp|net.FlagLoopback)
 		if ifi != nil {
 			cm.IfIndex = ifi.Index
 		}
@@ -91,7 +91,8 @@ func BenchmarkPacketConnReadWriteUnicast(b *testing.B) {
 	cm := ipv4.ControlMessage{
 		Src: net.IPv4(127, 0, 0, 1),
 	}
-	if ifi := nettest.RoutedInterface("ip4", net.FlagUp|net.FlagLoopback); ifi != nil {
+	ifi, _ := nettest.RoutedInterface("ip4", net.FlagUp|net.FlagLoopback)
+	if ifi != nil {
 		cm.IfIndex = ifi.Index
 	}
 
@@ -231,12 +232,12 @@ func TestPacketConnConcurrentReadWriteUnicastUDP(t *testing.T) {
 	defer p.Close()
 
 	dst := c.LocalAddr()
-	ifi := nettest.RoutedInterface("ip4", net.FlagUp|net.FlagLoopback)
+	ifi, _ := nettest.RoutedInterface("ip4", net.FlagUp|net.FlagLoopback)
 	cf := ipv4.FlagTTL | ipv4.FlagSrc | ipv4.FlagDst | ipv4.FlagInterface
 	wb := []byte("HELLO-R-U-THERE")
 
 	if err := p.SetControlMessage(cf, true); err != nil { // probe before test
-		if nettest.ProtocolNotSupported(err) {
+		if protocolNotSupported(err) {
 			t.Skipf("not supported on %s", runtime.GOOS)
 		}
 		t.Fatal(err)
@@ -358,11 +359,11 @@ func TestPacketConnConcurrentReadWriteUnicast(t *testing.T) {
 func testPacketConnConcurrentReadWriteUnicast(t *testing.T, p *ipv4.PacketConn, data []byte, dst net.Addr, batch bool) {
 	t.Helper()
 
-	ifi := nettest.RoutedInterface("ip4", net.FlagUp|net.FlagLoopback)
+	ifi, _ := nettest.RoutedInterface("ip4", net.FlagUp|net.FlagLoopback)
 	cf := ipv4.FlagTTL | ipv4.FlagSrc | ipv4.FlagDst | ipv4.FlagInterface
 
 	if err := p.SetControlMessage(cf, true); err != nil { // probe before test
-		if nettest.ProtocolNotSupported(err) {
+		if protocolNotSupported(err) {
 			t.Skipf("not supported on %s", runtime.GOOS)
 		}
 		t.Fatal(err)
diff --git a/ipv4/unicast_test.go b/ipv4/unicast_test.go
index a75f54ea..a4ddfb7c 100644
--- a/ipv4/unicast_test.go
+++ b/ipv4/unicast_test.go
@@ -14,8 +14,8 @@ import (
 
 	"golang.org/x/net/icmp"
 	"golang.org/x/net/internal/iana"
-	"golang.org/x/net/internal/nettest"
 	"golang.org/x/net/ipv4"
+	"golang.org/x/net/nettest"
 )
 
 func TestPacketConnReadWriteUnicastUDP(t *testing.T) {
@@ -23,8 +23,7 @@ func TestPacketConnReadWriteUnicastUDP(t *testing.T) {
 	case "aix", "fuchsia", "hurd", "js", "nacl", "plan9", "windows":
 		t.Skipf("not supported on %s", runtime.GOOS)
 	}
-	ifi := nettest.RoutedInterface("ip4", net.FlagUp|net.FlagLoopback)
-	if ifi == nil {
+	if _, err := nettest.RoutedInterface("ip4", net.FlagUp|net.FlagLoopback); err != nil {
 		t.Skipf("not available on %s", runtime.GOOS)
 	}
 
@@ -42,7 +41,7 @@ func TestPacketConnReadWriteUnicastUDP(t *testing.T) {
 
 	for i, toggle := range []bool{true, false, true} {
 		if err := p.SetControlMessage(cf, toggle); err != nil {
-			if nettest.ProtocolNotSupported(err) {
+			if protocolNotSupported(err) {
 				t.Logf("not supported on %s", runtime.GOOS)
 				continue
 			}
@@ -74,11 +73,10 @@ func TestPacketConnReadWriteUnicastICMP(t *testing.T) {
 	case "aix", "fuchsia", "hurd", "js", "nacl", "plan9", "windows":
 		t.Skipf("not supported on %s", runtime.GOOS)
 	}
-	if m, ok := nettest.SupportsRawIPSocket(); !ok {
-		t.Skip(m)
+	if !nettest.SupportsRawSocket() {
+		t.Skipf("not supported on %s/%s", runtime.GOOS, runtime.GOARCH)
 	}
-	ifi := nettest.RoutedInterface("ip4", net.FlagUp|net.FlagLoopback)
-	if ifi == nil {
+	if _, err := nettest.RoutedInterface("ip4", net.FlagUp|net.FlagLoopback); err != nil {
 		t.Skipf("not available on %s", runtime.GOOS)
 	}
 
@@ -112,7 +110,7 @@ func TestPacketConnReadWriteUnicastICMP(t *testing.T) {
 			t.Fatal(err)
 		}
 		if err := p.SetControlMessage(cf, toggle); err != nil {
-			if nettest.ProtocolNotSupported(err) {
+			if protocolNotSupported(err) {
 				t.Logf("not supported on %s", runtime.GOOS)
 				continue
 			}
@@ -160,11 +158,10 @@ func TestRawConnReadWriteUnicastICMP(t *testing.T) {
 	case "aix", "fuchsia", "hurd", "js", "nacl", "plan9", "windows":
 		t.Skipf("not supported on %s", runtime.GOOS)
 	}
-	if m, ok := nettest.SupportsRawIPSocket(); !ok {
-		t.Skip(m)
+	if !nettest.SupportsRawSocket() {
+		t.Skipf("not supported on %s/%s", runtime.GOOS, runtime.GOARCH)
 	}
-	ifi := nettest.RoutedInterface("ip4", net.FlagUp|net.FlagLoopback)
-	if ifi == nil {
+	if _, err := nettest.RoutedInterface("ip4", net.FlagUp|net.FlagLoopback); err != nil {
 		t.Skipf("not available on %s", runtime.GOOS)
 	}
 
@@ -206,7 +203,7 @@ func TestRawConnReadWriteUnicastICMP(t *testing.T) {
 			Dst:      dst.IP,
 		}
 		if err := r.SetControlMessage(cf, toggle); err != nil {
-			if nettest.ProtocolNotSupported(err) {
+			if protocolNotSupported(err) {
 				t.Logf("not supported on %s", runtime.GOOS)
 				continue
 			}
diff --git a/ipv4/unicastsockopt_test.go b/ipv4/unicastsockopt_test.go
index 9a279b7d..7ff9acc2 100644
--- a/ipv4/unicastsockopt_test.go
+++ b/ipv4/unicastsockopt_test.go
@@ -10,8 +10,8 @@ import (
 	"testing"
 
 	"golang.org/x/net/internal/iana"
-	"golang.org/x/net/internal/nettest"
 	"golang.org/x/net/ipv4"
+	"golang.org/x/net/nettest"
 )
 
 func TestConnUnicastSocketOptions(t *testing.T) {
@@ -19,8 +19,7 @@ func TestConnUnicastSocketOptions(t *testing.T) {
 	case "aix", "fuchsia", "hurd", "js", "nacl", "plan9", "windows":
 		t.Skipf("not supported on %s", runtime.GOOS)
 	}
-	ifi := nettest.RoutedInterface("ip4", net.FlagUp|net.FlagLoopback)
-	if ifi == nil {
+	if _, err := nettest.RoutedInterface("ip4", net.FlagUp|net.FlagLoopback); err != nil {
 		t.Skipf("not available on %s", runtime.GOOS)
 	}
 
@@ -65,15 +64,14 @@ func TestPacketConnUnicastSocketOptions(t *testing.T) {
 	case "aix", "fuchsia", "hurd", "js", "nacl", "plan9", "windows":
 		t.Skipf("not supported on %s", runtime.GOOS)
 	}
-	ifi := nettest.RoutedInterface("ip4", net.FlagUp|net.FlagLoopback)
-	if ifi == nil {
+	if _, err := nettest.RoutedInterface("ip4", net.FlagUp|net.FlagLoopback); err != nil {
 		t.Skipf("not available on %s", runtime.GOOS)
 	}
 
-	m, ok := nettest.SupportsRawIPSocket()
+	ok := nettest.SupportsRawSocket()
 	for _, tt := range packetConnUnicastSocketOptionTests {
 		if tt.net == "ip4" && !ok {
-			t.Log(m)
+			t.Logf("not supported on %s/%s", runtime.GOOS, runtime.GOARCH)
 			continue
 		}
 		c, err := net.ListenPacket(tt.net+tt.proto, tt.addr)
@@ -91,11 +89,10 @@ func TestRawConnUnicastSocketOptions(t *testing.T) {
 	case "aix", "fuchsia", "hurd", "js", "nacl", "plan9", "windows":
 		t.Skipf("not supported on %s", runtime.GOOS)
 	}
-	if m, ok := nettest.SupportsRawIPSocket(); !ok {
-		t.Skip(m)
+	if !nettest.SupportsRawSocket() {
+		t.Skipf("not supported on %s/%s", runtime.GOOS, runtime.GOARCH)
 	}
-	ifi := nettest.RoutedInterface("ip4", net.FlagUp|net.FlagLoopback)
-	if ifi == nil {
+	if _, err := nettest.RoutedInterface("ip4", net.FlagUp|net.FlagLoopback); err != nil {
 		t.Skipf("not available on %s", runtime.GOOS)
 	}
 
diff --git a/ipv6/bpf_test.go b/ipv6/bpf_test.go
index 8253e1f4..e249e1c9 100644
--- a/ipv6/bpf_test.go
+++ b/ipv6/bpf_test.go
@@ -12,13 +12,14 @@ import (
 
 	"golang.org/x/net/bpf"
 	"golang.org/x/net/ipv6"
+	"golang.org/x/net/nettest"
 )
 
 func TestBPF(t *testing.T) {
 	if runtime.GOOS != "linux" {
 		t.Skipf("not supported on %s", runtime.GOOS)
 	}
-	if !supportsIPv6 {
+	if !nettest.SupportsIPv6() {
 		t.Skip("ipv6 is not supported")
 	}
 
diff --git a/ipv6/helper_posix_test.go b/ipv6/helper_posix_test.go
new file mode 100644
index 00000000..cc85cea3
--- /dev/null
+++ b/ipv6/helper_posix_test.go
@@ -0,0 +1,31 @@
+// Copyright 2014 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// +build aix darwin dragonfly freebsd linux netbsd openbsd solaris windows
+
+package ipv6_test
+
+import (
+	"os"
+	"syscall"
+)
+
+func protocolNotSupported(err error) bool {
+	switch err := err.(type) {
+	case syscall.Errno:
+		switch err {
+		case syscall.EPROTONOSUPPORT, syscall.ENOPROTOOPT:
+			return true
+		}
+	case *os.SyscallError:
+		switch err := err.Err.(type) {
+		case syscall.Errno:
+			switch err {
+			case syscall.EPROTONOSUPPORT, syscall.ENOPROTOOPT:
+				return true
+			}
+		}
+	}
+	return false
+}
diff --git a/ipv6/helper_stub_test.go b/ipv6/helper_stub_test.go
new file mode 100644
index 00000000..cc515d1b
--- /dev/null
+++ b/ipv6/helper_stub_test.go
@@ -0,0 +1,20 @@
+// Copyright 2014 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// +build !aix,!darwin,!dragonfly,!freebsd,!linux,!netbsd,!openbsd,!solaris,!windows
+
+package ipv6_test
+
+import (
+	"fmt"
+	"runtime"
+)
+
+func supportsIPv6MulticastDeliveryOnLoopback() (string, bool) {
+	return fmt.Sprintf("not supported on %s/%s", runtime.GOOS, runtime.GOARCH), false
+}
+
+func protocolNotSupported(err error) bool {
+	return false
+}
diff --git a/internal/nettest/helper_bsd.go b/ipv6/helper_unix_test.go
similarity index 54%
rename from internal/nettest/helper_bsd.go
rename to ipv6/helper_unix_test.go
index 4025bd28..d94d912a 100644
--- a/internal/nettest/helper_bsd.go
+++ b/ipv6/helper_unix_test.go
@@ -1,24 +1,25 @@
-// Copyright 2016 The Go Authors. All rights reserved.
+// Copyright 2015 The Go Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build darwin dragonfly freebsd netbsd openbsd
+// +build aix darwin dragonfly freebsd linux netbsd openbsd solaris
 
-package nettest
+package ipv6_test
 
 import (
+	"fmt"
 	"runtime"
 )
 
-func supportsIPv6MulticastDeliveryOnLoopback() bool {
+func supportsIPv6MulticastDeliveryOnLoopback() (string, bool) {
 	switch runtime.GOOS {
 	case "freebsd":
 		// See http://www.freebsd.org/cgi/query-pr.cgi?pr=180065.
 		// Even after the fix, it looks like the latest
 		// kernels don't deliver link-local scoped multicast
 		// packets correctly.
-		return false
+		return fmt.Sprintf("not supported on %s/%s", runtime.GOOS, runtime.GOARCH), false
 	default:
-		return true
+		return "", true
 	}
 }
diff --git a/ipv6/helper_windows_test.go b/ipv6/helper_windows_test.go
new file mode 100644
index 00000000..329cfde9
--- /dev/null
+++ b/ipv6/helper_windows_test.go
@@ -0,0 +1,9 @@
+// Copyright 2015 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package ipv6_test
+
+func supportsIPv6MulticastDeliveryOnLoopback() (string, bool) {
+	return "", true
+}
diff --git a/ipv6/icmp_test.go b/ipv6/icmp_test.go
index 940a7aa8..c4b59042 100644
--- a/ipv6/icmp_test.go
+++ b/ipv6/icmp_test.go
@@ -10,8 +10,8 @@ import (
 	"runtime"
 	"testing"
 
-	"golang.org/x/net/internal/nettest"
 	"golang.org/x/net/ipv6"
+	"golang.org/x/net/nettest"
 )
 
 var icmpStringTests = []struct {
@@ -64,11 +64,11 @@ func TestSetICMPFilter(t *testing.T) {
 	case "aix", "fuchsia", "hurd", "js", "nacl", "plan9", "windows":
 		t.Skipf("not supported on %s", runtime.GOOS)
 	}
-	if !supportsIPv6 {
+	if !nettest.SupportsIPv6() {
 		t.Skip("ipv6 is not supported")
 	}
-	if m, ok := nettest.SupportsRawIPSocket(); !ok {
-		t.Skip(m)
+	if !nettest.SupportsRawSocket() {
+		t.Skipf("not supported on %s/%s", runtime.GOOS, runtime.GOARCH)
 	}
 
 	c, err := net.ListenPacket("ip6:ipv6-icmp", "::1")
diff --git a/ipv6/multicast_test.go b/ipv6/multicast_test.go
index 6ca6fd1c..8331e27b 100644
--- a/ipv6/multicast_test.go
+++ b/ipv6/multicast_test.go
@@ -14,8 +14,8 @@ import (
 
 	"golang.org/x/net/icmp"
 	"golang.org/x/net/internal/iana"
-	"golang.org/x/net/internal/nettest"
 	"golang.org/x/net/ipv6"
+	"golang.org/x/net/nettest"
 )
 
 var packetConnReadWriteMulticastUDPTests = []struct {
@@ -32,14 +32,14 @@ func TestPacketConnReadWriteMulticastUDP(t *testing.T) {
 	case "aix", "fuchsia", "hurd", "js", "nacl", "plan9", "windows":
 		t.Skipf("not supported on %s", runtime.GOOS)
 	}
-	if !supportsIPv6 {
+	if !nettest.SupportsIPv6() {
 		t.Skip("ipv6 is not supported")
 	}
-	if !nettest.SupportsIPv6MulticastDeliveryOnLoopback() {
-		t.Skipf("multicast delivery doesn't work correctly on %s", runtime.GOOS)
+	if m, ok := supportsIPv6MulticastDeliveryOnLoopback(); !ok {
+		t.Skip(m)
 	}
-	ifi := nettest.RoutedInterface("ip6", net.FlagUp|net.FlagMulticast|net.FlagLoopback)
-	if ifi == nil {
+	ifi, err := nettest.RoutedInterface("ip6", net.FlagUp|net.FlagMulticast|net.FlagLoopback)
+	if err != nil {
 		t.Skipf("not available on %s", runtime.GOOS)
 	}
 
@@ -94,7 +94,7 @@ func TestPacketConnReadWriteMulticastUDP(t *testing.T) {
 
 		for i, toggle := range []bool{true, false, true} {
 			if err := p.SetControlMessage(cf, toggle); err != nil {
-				if nettest.ProtocolNotSupported(err) {
+				if protocolNotSupported(err) {
 					t.Logf("not supported on %s", runtime.GOOS)
 					continue
 				}
@@ -132,17 +132,17 @@ func TestPacketConnReadWriteMulticastICMP(t *testing.T) {
 	case "aix", "fuchsia", "hurd", "js", "nacl", "plan9", "windows":
 		t.Skipf("not supported on %s", runtime.GOOS)
 	}
-	if !supportsIPv6 {
+	if !nettest.SupportsIPv6() {
 		t.Skip("ipv6 is not supported")
 	}
-	if !nettest.SupportsIPv6MulticastDeliveryOnLoopback() {
-		t.Skipf("multicast delivery doesn't work correctly on %s", runtime.GOOS)
-	}
-	if m, ok := nettest.SupportsRawIPSocket(); !ok {
+	if m, ok := supportsIPv6MulticastDeliveryOnLoopback(); !ok {
 		t.Skip(m)
 	}
-	ifi := nettest.RoutedInterface("ip6", net.FlagUp|net.FlagMulticast|net.FlagLoopback)
-	if ifi == nil {
+	if !nettest.SupportsRawSocket() {
+		t.Skipf("not supported on %s/%s", runtime.GOOS, runtime.GOARCH)
+	}
+	ifi, err := nettest.RoutedInterface("ip6", net.FlagUp|net.FlagMulticast|net.FlagLoopback)
+	if err != nil {
 		t.Skipf("not available on %s", runtime.GOOS)
 	}
 
@@ -229,7 +229,7 @@ func TestPacketConnReadWriteMulticastICMP(t *testing.T) {
 				t.Fatal(err)
 			}
 			if err := p.SetControlMessage(cf, toggle); err != nil {
-				if nettest.ProtocolNotSupported(err) {
+				if protocolNotSupported(err) {
 					t.Logf("not supported on %s", runtime.GOOS)
 					continue
 				}
diff --git a/ipv6/multicastlistener_test.go b/ipv6/multicastlistener_test.go
index 91d2b1df..9ca5359b 100644
--- a/ipv6/multicastlistener_test.go
+++ b/ipv6/multicastlistener_test.go
@@ -9,8 +9,8 @@ import (
 	"runtime"
 	"testing"
 
-	"golang.org/x/net/internal/nettest"
 	"golang.org/x/net/ipv6"
+	"golang.org/x/net/nettest"
 )
 
 var udpMultipleGroupListenerTests = []net.Addr{
@@ -24,7 +24,7 @@ func TestUDPSinglePacketConnWithMultipleGroupListeners(t *testing.T) {
 	case "aix", "fuchsia", "hurd", "js", "nacl", "plan9", "windows":
 		t.Skipf("not supported on %s", runtime.GOOS)
 	}
-	if !supportsIPv6 {
+	if !nettest.SupportsIPv6() {
 		t.Skip("ipv6 is not supported")
 	}
 
@@ -43,7 +43,7 @@ func TestUDPSinglePacketConnWithMultipleGroupListeners(t *testing.T) {
 			t.Fatal(err)
 		}
 		for i, ifi := range ift {
-			if _, ok := nettest.IsMulticastCapable("ip6", &ifi); !ok {
+			if _, err := nettest.MulticastSource("ip6", &ifi); err != nil {
 				continue
 			}
 			if err := p.JoinGroup(&ifi, gaddr); err != nil {
@@ -64,7 +64,7 @@ func TestUDPMultiplePacketConnWithMultipleGroupListeners(t *testing.T) {
 	case "aix", "fuchsia", "hurd", "js", "nacl", "plan9", "windows":
 		t.Skipf("not supported on %s", runtime.GOOS)
 	}
-	if !supportsIPv6 {
+	if !nettest.SupportsIPv6() {
 		t.Skip("ipv6 is not supported")
 	}
 
@@ -94,7 +94,7 @@ func TestUDPMultiplePacketConnWithMultipleGroupListeners(t *testing.T) {
 			t.Fatal(err)
 		}
 		for i, ifi := range ift {
-			if _, ok := nettest.IsMulticastCapable("ip6", &ifi); !ok {
+			if _, err := nettest.MulticastSource("ip6", &ifi); err != nil {
 				continue
 			}
 			for _, p := range ps {
@@ -119,7 +119,7 @@ func TestUDPPerInterfaceSinglePacketConnWithSingleGroupListener(t *testing.T) {
 	case "aix", "fuchsia", "hurd", "js", "nacl", "plan9", "windows":
 		t.Skipf("not supported on %s", runtime.GOOS)
 	}
-	if !supportsIPv6 {
+	if !nettest.SupportsIPv6() {
 		t.Skip("ipv6 is not supported")
 	}
 
@@ -136,8 +136,8 @@ func TestUDPPerInterfaceSinglePacketConnWithSingleGroupListener(t *testing.T) {
 	}
 	port := "0"
 	for i, ifi := range ift {
-		ip, ok := nettest.IsMulticastCapable("ip6", &ifi)
-		if !ok {
+		ip, err := nettest.MulticastSource("ip6", &ifi)
+		if err != nil {
 			continue
 		}
 		c, err := net.ListenPacket("udp6", net.JoinHostPort(ip.String()+"%"+ifi.Name, port)) // unicast address with non-reusable port
@@ -175,11 +175,11 @@ func TestIPSinglePacketConnWithSingleGroupListener(t *testing.T) {
 	case "aix", "fuchsia", "hurd", "js", "nacl", "plan9", "windows":
 		t.Skipf("not supported on %s", runtime.GOOS)
 	}
-	if !supportsIPv6 {
+	if !nettest.SupportsIPv6() {
 		t.Skip("ipv6 is not supported")
 	}
-	if m, ok := nettest.SupportsRawIPSocket(); !ok {
-		t.Skip(m)
+	if !nettest.SupportsRawSocket() {
+		t.Skipf("not supported on %s/%s", runtime.GOOS, runtime.GOARCH)
 	}
 
 	c, err := net.ListenPacket("ip6:ipv6-icmp", "::") // wildcard address
@@ -197,7 +197,7 @@ func TestIPSinglePacketConnWithSingleGroupListener(t *testing.T) {
 		t.Fatal(err)
 	}
 	for i, ifi := range ift {
-		if _, ok := nettest.IsMulticastCapable("ip6", &ifi); !ok {
+		if _, err := nettest.MulticastSource("ip6", &ifi); err != nil {
 			continue
 		}
 		if err := p.JoinGroup(&ifi, &gaddr); err != nil {
@@ -219,11 +219,11 @@ func TestIPPerInterfaceSinglePacketConnWithSingleGroupListener(t *testing.T) {
 	case "aix", "fuchsia", "hurd", "js", "nacl", "plan9", "windows":
 		t.Skipf("not supported on %s", runtime.GOOS)
 	}
-	if !supportsIPv6 {
+	if !nettest.SupportsIPv6() {
 		t.Skip("ipv6 is not supported")
 	}
-	if m, ok := nettest.SupportsRawIPSocket(); !ok {
-		t.Skip(m)
+	if !nettest.SupportsRawSocket() {
+		t.Skipf("not supported on %s/%s", runtime.GOOS, runtime.GOARCH)
 	}
 
 	gaddr := net.IPAddr{IP: net.ParseIP("ff02::114")} // see RFC 4727
@@ -238,8 +238,8 @@ func TestIPPerInterfaceSinglePacketConnWithSingleGroupListener(t *testing.T) {
 		t.Fatal(err)
 	}
 	for i, ifi := range ift {
-		ip, ok := nettest.IsMulticastCapable("ip6", &ifi)
-		if !ok {
+		ip, err := nettest.MulticastSource("ip6", &ifi)
+		if err != nil {
 			continue
 		}
 		c, err := net.ListenPacket("ip6:ipv6-icmp", ip.String()+"%"+ifi.Name) // unicast address
diff --git a/ipv6/multicastsockopt_test.go b/ipv6/multicastsockopt_test.go
index 2cb2da2d..a3999457 100644
--- a/ipv6/multicastsockopt_test.go
+++ b/ipv6/multicastsockopt_test.go
@@ -9,8 +9,8 @@ import (
 	"runtime"
 	"testing"
 
-	"golang.org/x/net/internal/nettest"
 	"golang.org/x/net/ipv6"
+	"golang.org/x/net/nettest"
 )
 
 var packetConnMulticastSocketOptionTests = []struct {
@@ -29,18 +29,18 @@ func TestPacketConnMulticastSocketOptions(t *testing.T) {
 	case "aix", "fuchsia", "hurd", "js", "nacl", "plan9", "windows":
 		t.Skipf("not supported on %s", runtime.GOOS)
 	}
-	if !supportsIPv6 {
+	if !nettest.SupportsIPv6() {
 		t.Skip("ipv6 is not supported")
 	}
-	ifi := nettest.RoutedInterface("ip6", net.FlagUp|net.FlagMulticast|net.FlagLoopback)
-	if ifi == nil {
+	ifi, err := nettest.RoutedInterface("ip6", net.FlagUp|net.FlagMulticast|net.FlagLoopback)
+	if err != nil {
 		t.Skipf("not available on %s", runtime.GOOS)
 	}
 
-	m, ok := nettest.SupportsRawIPSocket()
+	ok := nettest.SupportsRawSocket()
 	for _, tt := range packetConnMulticastSocketOptionTests {
 		if tt.net == "ip6" && !ok {
-			t.Log(m)
+			t.Logf("not supported on %s/%s", runtime.GOOS, runtime.GOARCH)
 			continue
 		}
 		c, err := net.ListenPacket(tt.net+tt.proto, tt.addr)
diff --git a/ipv6/readwrite_test.go b/ipv6/readwrite_test.go
index 18d5f9d6..46bbf9de 100644
--- a/ipv6/readwrite_test.go
+++ b/ipv6/readwrite_test.go
@@ -14,8 +14,8 @@ import (
 	"testing"
 
 	"golang.org/x/net/internal/iana"
-	"golang.org/x/net/internal/nettest"
 	"golang.org/x/net/ipv6"
+	"golang.org/x/net/nettest"
 )
 
 func BenchmarkReadWriteUnicast(b *testing.B) {
@@ -53,7 +53,7 @@ func BenchmarkReadWriteUnicast(b *testing.B) {
 			TrafficClass: iana.DiffServAF11 | iana.CongestionExperienced,
 			HopLimit:     1,
 		}
-		ifi := nettest.RoutedInterface("ip6", net.FlagUp|net.FlagLoopback)
+		ifi, _ := nettest.RoutedInterface("ip6", net.FlagUp|net.FlagLoopback)
 		if ifi != nil {
 			cm.IfIndex = ifi.Index
 		}
@@ -91,7 +91,8 @@ func BenchmarkPacketConnReadWriteUnicast(b *testing.B) {
 		HopLimit:     1,
 		Src:          net.IPv6loopback,
 	}
-	if ifi := nettest.RoutedInterface("ip6", net.FlagUp|net.FlagLoopback); ifi != nil {
+	ifi, _ := nettest.RoutedInterface("ip6", net.FlagUp|net.FlagLoopback)
+	if ifi != nil {
 		cm.IfIndex = ifi.Index
 	}
 
@@ -221,7 +222,7 @@ func TestPacketConnConcurrentReadWriteUnicastUDP(t *testing.T) {
 	case "aix", "fuchsia", "hurd", "js", "nacl", "plan9", "windows":
 		t.Skipf("not supported on %s", runtime.GOOS)
 	}
-	if !supportsIPv6 {
+	if !nettest.SupportsIPv6() {
 		t.Skip("ipv6 is not supported")
 	}
 
@@ -234,12 +235,12 @@ func TestPacketConnConcurrentReadWriteUnicastUDP(t *testing.T) {
 	defer p.Close()
 
 	dst := c.LocalAddr()
-	ifi := nettest.RoutedInterface("ip6", net.FlagUp|net.FlagLoopback)
+	ifi, _ := nettest.RoutedInterface("ip6", net.FlagUp|net.FlagLoopback)
 	cf := ipv6.FlagTrafficClass | ipv6.FlagHopLimit | ipv6.FlagSrc | ipv6.FlagDst | ipv6.FlagInterface | ipv6.FlagPathMTU
 	wb := []byte("HELLO-R-U-THERE")
 
 	if err := p.SetControlMessage(cf, true); err != nil { // probe before test
-		if nettest.ProtocolNotSupported(err) {
+		if protocolNotSupported(err) {
 			t.Skipf("not supported on %s", runtime.GOOS)
 		}
 		t.Fatal(err)
@@ -357,11 +358,11 @@ func TestPacketConnConcurrentReadWriteUnicast(t *testing.T) {
 func testPacketConnConcurrentReadWriteUnicast(t *testing.T, p *ipv6.PacketConn, data []byte, dst net.Addr, batch bool) {
 	t.Helper()
 
-	ifi := nettest.RoutedInterface("ip6", net.FlagUp|net.FlagLoopback)
+	ifi, _ := nettest.RoutedInterface("ip6", net.FlagUp|net.FlagLoopback)
 	cf := ipv6.FlagTrafficClass | ipv6.FlagHopLimit | ipv6.FlagSrc | ipv6.FlagDst | ipv6.FlagInterface | ipv6.FlagPathMTU
 
 	if err := p.SetControlMessage(cf, true); err != nil { // probe before test
-		if nettest.ProtocolNotSupported(err) {
+		if protocolNotSupported(err) {
 			t.Skipf("not supported on %s", runtime.GOOS)
 		}
 		t.Fatal(err)
diff --git a/ipv6/sockopt_test.go b/ipv6/sockopt_test.go
index 0ff911d4..a438c694 100644
--- a/ipv6/sockopt_test.go
+++ b/ipv6/sockopt_test.go
@@ -11,18 +11,16 @@ import (
 	"testing"
 
 	"golang.org/x/net/internal/iana"
-	"golang.org/x/net/internal/nettest"
 	"golang.org/x/net/ipv6"
+	"golang.org/x/net/nettest"
 )
 
-var supportsIPv6 bool = nettest.SupportsIPv6()
-
 func TestConnInitiatorPathMTU(t *testing.T) {
 	switch runtime.GOOS {
 	case "aix", "fuchsia", "hurd", "js", "nacl", "plan9", "windows":
 		t.Skipf("not supported on %s", runtime.GOOS)
 	}
-	if !supportsIPv6 {
+	if !nettest.SupportsIPv6() {
 		t.Skip("ipv6 is not supported")
 	}
 
@@ -60,7 +58,7 @@ func TestConnResponderPathMTU(t *testing.T) {
 	case "aix", "fuchsia", "hurd", "js", "nacl", "plan9", "windows":
 		t.Skipf("not supported on %s", runtime.GOOS)
 	}
-	if !supportsIPv6 {
+	if !nettest.SupportsIPv6() {
 		t.Skip("ipv6 is not supported")
 	}
 
@@ -98,11 +96,11 @@ func TestPacketConnChecksum(t *testing.T) {
 	case "aix", "fuchsia", "hurd", "js", "nacl", "plan9", "windows":
 		t.Skipf("not supported on %s", runtime.GOOS)
 	}
-	if !supportsIPv6 {
+	if !nettest.SupportsIPv6() {
 		t.Skip("ipv6 is not supported")
 	}
-	if m, ok := nettest.SupportsRawIPSocket(); !ok {
-		t.Skip(m)
+	if !nettest.SupportsRawSocket() {
+		t.Skipf("not supported on %s/%s", runtime.GOOS, runtime.GOARCH)
 	}
 
 	c, err := net.ListenPacket(fmt.Sprintf("ip6:%d", iana.ProtocolOSPFIGP), "::") // OSPF for IPv6
diff --git a/ipv6/unicast_test.go b/ipv6/unicast_test.go
index 25fb4eb2..15831f96 100644
--- a/ipv6/unicast_test.go
+++ b/ipv6/unicast_test.go
@@ -14,8 +14,8 @@ import (
 
 	"golang.org/x/net/icmp"
 	"golang.org/x/net/internal/iana"
-	"golang.org/x/net/internal/nettest"
 	"golang.org/x/net/ipv6"
+	"golang.org/x/net/nettest"
 )
 
 func TestPacketConnReadWriteUnicastUDP(t *testing.T) {
@@ -23,7 +23,7 @@ func TestPacketConnReadWriteUnicastUDP(t *testing.T) {
 	case "aix", "fuchsia", "hurd", "js", "nacl", "plan9", "windows":
 		t.Skipf("not supported on %s", runtime.GOOS)
 	}
-	if !supportsIPv6 {
+	if !nettest.SupportsIPv6() {
 		t.Skip("ipv6 is not supported")
 	}
 
@@ -41,7 +41,7 @@ func TestPacketConnReadWriteUnicastUDP(t *testing.T) {
 		Src:          net.IPv6loopback,
 	}
 	cf := ipv6.FlagTrafficClass | ipv6.FlagHopLimit | ipv6.FlagSrc | ipv6.FlagDst | ipv6.FlagInterface | ipv6.FlagPathMTU
-	ifi := nettest.RoutedInterface("ip6", net.FlagUp|net.FlagLoopback)
+	ifi, _ := nettest.RoutedInterface("ip6", net.FlagUp|net.FlagLoopback)
 	if ifi != nil {
 		cm.IfIndex = ifi.Index
 	}
@@ -49,7 +49,7 @@ func TestPacketConnReadWriteUnicastUDP(t *testing.T) {
 
 	for i, toggle := range []bool{true, false, true} {
 		if err := p.SetControlMessage(cf, toggle); err != nil {
-			if nettest.ProtocolNotSupported(err) {
+			if protocolNotSupported(err) {
 				t.Logf("not supported on %s", runtime.GOOS)
 				continue
 			}
@@ -81,11 +81,11 @@ func TestPacketConnReadWriteUnicastICMP(t *testing.T) {
 	case "aix", "fuchsia", "hurd", "js", "nacl", "plan9", "windows":
 		t.Skipf("not supported on %s", runtime.GOOS)
 	}
-	if !supportsIPv6 {
+	if !nettest.SupportsIPv6() {
 		t.Skip("ipv6 is not supported")
 	}
-	if m, ok := nettest.SupportsRawIPSocket(); !ok {
-		t.Skip(m)
+	if !nettest.SupportsRawSocket() {
+		t.Skipf("not supported on %s/%s", runtime.GOOS, runtime.GOARCH)
 	}
 
 	c, err := net.ListenPacket("ip6:ipv6-icmp", "::1")
@@ -107,7 +107,7 @@ func TestPacketConnReadWriteUnicastICMP(t *testing.T) {
 		Src:          net.IPv6loopback,
 	}
 	cf := ipv6.FlagTrafficClass | ipv6.FlagHopLimit | ipv6.FlagSrc | ipv6.FlagDst | ipv6.FlagInterface | ipv6.FlagPathMTU
-	ifi := nettest.RoutedInterface("ip6", net.FlagUp|net.FlagLoopback)
+	ifi, _ := nettest.RoutedInterface("ip6", net.FlagUp|net.FlagLoopback)
 	if ifi != nil {
 		cm.IfIndex = ifi.Index
 	}
@@ -147,7 +147,7 @@ func TestPacketConnReadWriteUnicastICMP(t *testing.T) {
 			t.Fatal(err)
 		}
 		if err := p.SetControlMessage(cf, toggle); err != nil {
-			if nettest.ProtocolNotSupported(err) {
+			if protocolNotSupported(err) {
 				t.Logf("not supported on %s", runtime.GOOS)
 				continue
 			}
diff --git a/ipv6/unicastsockopt_test.go b/ipv6/unicastsockopt_test.go
index 2f833736..84fdfd66 100644
--- a/ipv6/unicastsockopt_test.go
+++ b/ipv6/unicastsockopt_test.go
@@ -10,8 +10,8 @@ import (
 	"testing"
 
 	"golang.org/x/net/internal/iana"
-	"golang.org/x/net/internal/nettest"
 	"golang.org/x/net/ipv6"
+	"golang.org/x/net/nettest"
 )
 
 func TestConnUnicastSocketOptions(t *testing.T) {
@@ -19,7 +19,7 @@ func TestConnUnicastSocketOptions(t *testing.T) {
 	case "aix", "fuchsia", "hurd", "js", "nacl", "plan9", "windows":
 		t.Skipf("not supported on %s", runtime.GOOS)
 	}
-	if !supportsIPv6 {
+	if !nettest.SupportsIPv6() {
 		t.Skip("ipv6 is not supported")
 	}
 
@@ -64,14 +64,14 @@ func TestPacketConnUnicastSocketOptions(t *testing.T) {
 	case "aix", "fuchsia", "hurd", "js", "nacl", "plan9", "windows":
 		t.Skipf("not supported on %s", runtime.GOOS)
 	}
-	if !supportsIPv6 {
+	if !nettest.SupportsIPv6() {
 		t.Skip("ipv6 is not supported")
 	}
 
-	m, ok := nettest.SupportsRawIPSocket()
+	ok := nettest.SupportsRawSocket()
 	for _, tt := range packetConnUnicastSocketOptionTests {
 		if tt.net == "ip6" && !ok {
-			t.Log(m)
+			t.Logf("not supported on %s/%s", runtime.GOOS, runtime.GOARCH)
 			continue
 		}
 		c, err := net.ListenPacket(tt.net+tt.proto, tt.addr)
diff --git a/netutil/helper_stub_test.go b/netutil/helper_stub_test.go
new file mode 100644
index 00000000..6034aacc
--- /dev/null
+++ b/netutil/helper_stub_test.go
@@ -0,0 +1,11 @@
+// Copyright 2014 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// +build !aix,!darwin,!dragonfly,!freebsd,!linux,!netbsd,!openbsd,!solaris,!windows
+
+package netutil
+
+func maxOpenFiles() int {
+	return defaultMaxOpenFiles
+}
diff --git a/internal/nettest/helper_unix.go b/netutil/helper_unix_test.go
similarity index 65%
rename from internal/nettest/helper_unix.go
rename to netutil/helper_unix_test.go
index b6839dcd..fd712434 100644
--- a/internal/nettest/helper_unix.go
+++ b/netutil/helper_unix_test.go
@@ -4,14 +4,9 @@
 
 // +build aix darwin dragonfly freebsd linux netbsd openbsd solaris
 
-package nettest
+package netutil
 
-import (
-	"fmt"
-	"os"
-	"runtime"
-	"syscall"
-)
+import "syscall"
 
 func maxOpenFiles() int {
 	var rlim syscall.Rlimit
@@ -20,10 +15,3 @@ func maxOpenFiles() int {
 	}
 	return int(rlim.Cur)
 }
-
-func supportsRawIPSocket() (string, bool) {
-	if os.Getuid() != 0 {
-		return fmt.Sprintf("must be root on %s", runtime.GOOS), false
-	}
-	return "", true
-}
diff --git a/netutil/helper_windows_test.go b/netutil/helper_windows_test.go
new file mode 100644
index 00000000..8d5703d0
--- /dev/null
+++ b/netutil/helper_windows_test.go
@@ -0,0 +1,9 @@
+// Copyright 2015 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package netutil
+
+func maxOpenFiles() int {
+	return 4 * defaultMaxOpenFiles /* actually it's 16581375 */
+}
diff --git a/netutil/listen_test.go b/netutil/listen_test.go
index f40c9aa9..e00433d9 100644
--- a/netutil/listen_test.go
+++ b/netutil/listen_test.go
@@ -15,13 +15,13 @@ import (
 	"sync/atomic"
 	"testing"
 	"time"
-
-	"golang.org/x/net/internal/nettest"
 )
 
+const defaultMaxOpenFiles = 256
+
 func TestLimitListener(t *testing.T) {
 	const max = 5
-	attempts := (nettest.MaxOpenFiles() - max) / 2
+	attempts := (maxOpenFiles() - max) / 2
 	if attempts > 256 { // maximum length of accept queue is 128 by default
 		attempts = 256
 	}