net: skip interface tests when required external command not found

Fixes #4952.

R=alex.brainman
CC=golang-dev
https://golang.org/cl/7445046

src/pkg/net/interface_bsd_test.go

@@ -11,11 +11,11 @@ import (
 	"os/exec"
 )
 
-func (ti *testInterface) setBroadcast(suffix int) {
+func (ti *testInterface) setBroadcast(suffix int) error {
 	ti.name = fmt.Sprintf("vlan%d", suffix)
 	xname, err := exec.LookPath("ifconfig")
 	if err != nil {
-		xname = "ifconfig"
+		return err
 	}
 	ti.setupCmds = append(ti.setupCmds, &exec.Cmd{
 		Path: xname,
@@ -25,15 +25,16 @@ func (ti *testInterface) setBroadcast(suffix int) {
 		Path: xname,
 		Args: []string{"ifconfig", ti.name, "destroy"},
 	})
+	return nil
 }
 
-func (ti *testInterface) setPointToPoint(suffix int, local, remote string) {
+func (ti *testInterface) setPointToPoint(suffix int, local, remote string) error {
 	ti.name = fmt.Sprintf("gif%d", suffix)
 	ti.local = local
 	ti.remote = remote
 	xname, err := exec.LookPath("ifconfig")
 	if err != nil {
-		xname = "ifconfig"
+		return err
 	}
 	ti.setupCmds = append(ti.setupCmds, &exec.Cmd{
 		Path: xname,
@@ -47,4 +48,5 @@ func (ti *testInterface) setPointToPoint(suffix int, local, remote string) {
 		Path: xname,
 		Args: []string{"ifconfig", ti.name, "destroy"},
 	})
+	return nil
 }

src/pkg/net/interface_linux_test.go

@@ -10,11 +10,11 @@ import (
 	"testing"
 )
 
-func (ti *testInterface) setBroadcast(suffix int) {
+func (ti *testInterface) setBroadcast(suffix int) error {
 	ti.name = fmt.Sprintf("gotest%d", suffix)
 	xname, err := exec.LookPath("ip")
 	if err != nil {
-		xname = "ip"
+		return err
 	}
 	ti.setupCmds = append(ti.setupCmds, &exec.Cmd{
 		Path: xname,
@@ -24,15 +24,16 @@ func (ti *testInterface) setBroadcast(suffix int) {
 		Path: xname,
 		Args: []string{"ip", "link", "delete", ti.name, "type", "dummy"},
 	})
+	return nil
 }
 
-func (ti *testInterface) setPointToPoint(suffix int, local, remote string) {
+func (ti *testInterface) setPointToPoint(suffix int, local, remote string) error {
 	ti.name = fmt.Sprintf("gotest%d", suffix)
 	ti.local = local
 	ti.remote = remote
 	xname, err := exec.LookPath("ip")
 	if err != nil {
-		xname = "ip"
+		return err
 	}
 	ti.setupCmds = append(ti.setupCmds, &exec.Cmd{
 		Path: xname,
@@ -44,12 +45,13 @@ func (ti *testInterface) setPointToPoint(suffix int, local, remote string) {
 	})
 	xname, err = exec.LookPath("ifconfig")
 	if err != nil {
-		xname = "ifconfig"
+		return err
 	}
 	ti.setupCmds = append(ti.setupCmds, &exec.Cmd{
 		Path: xname,
 		Args: []string{"ifconfig", ti.name, "inet", local, "dstaddr", remote},
 	})
+	return nil
 }
 
 const (

src/pkg/net/interface_unix_test.go

@@ -53,7 +53,9 @@ func TestPointToPointInterface(t *testing.T) {
 	ip := ParseIP(remote)
 	for i := 0; i < 3; i++ {
 		ti := &testInterface{}
-		ti.setPointToPoint(5963+i, local, remote)
+		if err := ti.setPointToPoint(5963+i, local, remote); err != nil {
+			t.Skipf("test requries external command: %v", err)
+		}
 		if err := ti.setup(); err != nil {
 			t.Fatalf("testInterface.setup failed: %v", err)
 		} else {
@@ -98,7 +100,9 @@ func TestInterfaceArrivalAndDeparture(t *testing.T) {
 			t.Fatalf("Interfaces failed: %v", err)
 		}
 		ti := &testInterface{}
-		ti.setBroadcast(5682 + i)
+		if err := ti.setBroadcast(5682 + i); err != nil {
+			t.Skipf("test requires external command: %v", err)
+		}
 		if err := ti.setup(); err != nil {
 			t.Fatalf("testInterface.setup failed: %v", err)
 		} else {