Deflake TestIPv6DisableAllSysctl.

Earlier we were using waitForFileNotEmpty() which could return before the
container had completed running the "ip addr" program. Hence when processing
the partial results, the test would fail.

It is much easier to just use executeCombinedOutput() to pipe the output out.
It waits for the exec'd process to complete.

PiperOrigin-RevId: 770246387

Author: ayushr2

runsc/container/container_test.go

@@ -18,7 +18,6 @@ import (
 	"bytes"
 	"fmt"
 	"io"
-	"io/ioutil"
 	"math"
 	"math/rand"
 	"os"
@@ -4135,24 +4134,7 @@ func TestIPv6DisableAllSysctl(t *testing.T) {
 	for name, conf := range configs(t, true /* noOverlay */) {
 		for _, test := range tests {
 			t.Run(test.name+name, func(t *testing.T) {
-				dir, err := os.MkdirTemp(testutil.TmpDir(), "ipv6-test")
-				if err != nil {
-					t.Fatalf("os.MkdirTemp failed: %v", err)
-				}
-				defer os.RemoveAll(dir)
-				if err := os.Chmod(dir, 0777); err != nil {
-					t.Fatalf("error chmoding file: %q, %v", dir, err)
-				}
-
-				outputPath := filepath.Join(dir, "output")
-				outputFile, err := createWriteableOutputFile(outputPath)
-				if err != nil {
-					t.Fatalf("error creating output file: %v", err)
-				}
-				defer outputFile.Close()
-
-				script := fmt.Sprintf("ip addr >> %q", outputPath)
-				spec := testutil.NewSpecWithArgs("bash", "-c", script)
+				spec := testutil.NewSpecWithArgs("sleep", "infinity")
 				conf.Network = config.NetworkSandbox
 				if test.ipv6Disabled {
 					spec.Linux = &specs.Linux{}
@@ -4175,33 +4157,31 @@ func TestIPv6DisableAllSysctl(t *testing.T) {
 				if err != nil {
 					t.Fatalf("error creating container: %v", err)
 				}
+				defer cont.Destroy()
 				if err := cont.Start(conf); err != nil {
 					t.Fatalf("error starting container: %v", err)
 				}
 
-				// Wait until application has ran.
-				if err := waitForFileNotEmpty(outputFile); err != nil {
-					// This can happen when the network does not
-					// have any network interfaces configured.
-					// We cannot test whether the sysctl works
-					// properly in this case. Log a warning and
-					// return.
-					t.Logf("No network interfaces are configured: %v", err)
-					return
+				out, err := executeCombinedOutput(conf, cont, nil, "/bin/sh", "-c", "ip addr")
+				if err != nil {
+					t.Fatalf("error executing 'ip addr' command: %v", err)
 				}
 
-				content, err := ioutil.ReadFile(outputPath)
-				if err != nil {
-					fmt.Println("Error reading file:", err)
+				if len(out) == 0 {
+					// This can happen when the network does not have any network
+					// interfaces configured. We cannot test whether the sysctl works
+					// properly in this case. Log a warning and return.
+					t.Logf("No output from 'ip addr' command, no network interfaces are configured")
 					return
 				}
-				res := strings.Contains(string(content), "inet6")
+
+				res := strings.Contains(string(out), "inet6")
 				if test.ipv6Disabled && res {
-					t.Fatalf("IPv6 address present when IPv6 is disabled on all interfaces")
+					t.Errorf("IPv6 address present when IPv6 is disabled on all interfaces, output: %v", string(out))
 				}
 
 				if !test.ipv6Disabled && !res {
-					t.Fatalf("IPv6 address not present when IPv6 is enabled on all interfaces")
+					t.Errorf("IPv6 address not present when IPv6 is enabled on all interfaces, output: %v", string(out))
 				}
 			})
 		}