kubeadm: Don't hardcode temp path in a test

cmd/kubeadm/app/cmd/upgrade/common_test.go

@@ -18,11 +18,9 @@ package upgrade
 
 import (
 	"bytes"
-	"fmt"
 	"io/ioutil"
 	"os"
 	"testing"
-	"time"
 
 	kubeadmapi "k8s.io/kubernetes/cmd/kubeadm/app/apis/kubeadm"
 )
@@ -77,17 +75,25 @@ func TestGetK8sVersionFromUserInput(t *testing.T) {
 			name: "Version is optional",
 		},
 	}
-	for tnum, tt := range tcases {
+	for _, tt := range tcases {
 		t.Run(tt.name, func(t *testing.T) {
 			flags := &applyPlanFlags{}
 			if len(tt.clusterConfig) > 0 {
-				tmpfile := fmt.Sprintf("/tmp/kubeadm-upgrade-common-test-%d-%d.yaml", tnum, time.Now().Unix())
-				if err := ioutil.WriteFile(tmpfile, []byte(tt.clusterConfig), 0666); err != nil {
+				file, err := ioutil.TempFile("", "kubeadm-upgrade-common-test-*.yaml")
+				if err != nil {
 					t.Fatalf("Failed to create test config file: %+v", err)
 				}
-				defer os.Remove(tmpfile)
 
-				flags.cfgPath = tmpfile
+				tmpFileName := file.Name()
+				defer os.Remove(tmpFileName)
+
+				_, err = file.WriteString(tt.clusterConfig)
+				file.Close()
+				if err != nil {
+					t.Fatalf("Failed to write test config file contents: %+v", err)
+				}
+
+				flags.cfgPath = tmpFileName
 			}
 
 			userVersion, err := getK8sVersionFromUserInput(flags, tt.args, tt.isVersionMandatory)