kubeadm: include the err got from PrintDryRunFile

The error was ingored which means if anything wrong from `PrintDryRunFiles`,
it was sliently ignored.

Signed-off-by: Dave Chen <dave.chen@arm.com>

cmd/kubeadm/app/phases/upgrade/postupgrade.go

@@ -166,7 +166,7 @@ func writeKubeletConfigFiles(client clientset.Interface, cfg *kubeadmapi.InitCon
 	}
 
 	if dryRun { // Print what contents would be written
-		dryrunutil.PrintDryRunFile(kubeadmconstants.KubeletConfigurationFileName, kubeletDir, kubeadmconstants.KubeletRunDirectory, os.Stdout)
+		errs = append(errs, dryrunutil.PrintDryRunFile(kubeadmconstants.KubeletConfigurationFileName, kubeletDir, kubeadmconstants.KubeletRunDirectory, os.Stdout))
 	}
 	return errorsutil.NewAggregate(errs)
 }

cmd/kubeadm/app/phases/upgrade/postupgrade_test.go

@@ -19,12 +19,16 @@ package upgrade
 import (
 	"os"
 	"path/filepath"
+	"regexp"
 	"strings"
 	"testing"
 
 	"github.com/pkg/errors"
 
+	kubeadmapi "k8s.io/kubernetes/cmd/kubeadm/app/apis/kubeadm"
+	"k8s.io/kubernetes/cmd/kubeadm/app/componentconfigs"
 	"k8s.io/kubernetes/cmd/kubeadm/app/constants"
+	"k8s.io/kubernetes/cmd/kubeadm/app/preflight"
 	testutil "k8s.io/kubernetes/cmd/kubeadm/test"
 )
 
@@ -101,3 +105,104 @@ func TestRollbackFiles(t *testing.T) {
 		t.Fatalf("Expected error contains %q, got %v", errString, err)
 	}
 }
+
+func TestWriteKubeletConfigFiles(t *testing.T) {
+	// exit early if the user doesn't have root permission as the test needs to create /etc/kubernetes directory
+	// while the permission should be granted to the user.
+	isPrivileged := preflight.IsPrivilegedUserCheck{}
+	if _, err := isPrivileged.Check(); err != nil {
+		return
+	}
+	testCases := []struct {
+		name       string
+		dryrun     bool
+		patchesDir string
+		errPattern string
+		cfg        *kubeadmapi.InitConfiguration
+	}{
+		// Be careful that if the dryrun is set to false and the test is run on a live cluster, the kubelet config file might be overwritten.
+		// However, you should be able to find the original config file in /etc/kubernetes/tmp/kubeadm-kubelet-configxxx folder.
+		// The test haven't clean up the temporary file created under /etc/kubernetes/tmp/ as that could be accidentally delete other files in
+		// that folder as well which might be unexpected.
+		{
+			name:   "write kubelet config file successfully",
+			dryrun: true,
+			cfg: &kubeadmapi.InitConfiguration{
+				ClusterConfiguration: kubeadmapi.ClusterConfiguration{
+					ComponentConfigs: kubeadmapi.ComponentConfigMap{
+						componentconfigs.KubeletGroup: &componentConfig{},
+					},
+				},
+			},
+		},
+		{
+			name:       "aggregate errs: no kubelet config file and cannot read config file",
+			dryrun:     true,
+			errPattern: "no kubelet component config found.*no such file or directory",
+			cfg:        &kubeadmapi.InitConfiguration{},
+		},
+		{
+			name:       "only one err: patch dir does not exist",
+			dryrun:     true,
+			patchesDir: "Bogus",
+			errPattern: "could not list patch files for path \"Bogus\"",
+			cfg: &kubeadmapi.InitConfiguration{
+				ClusterConfiguration: kubeadmapi.ClusterConfiguration{
+					ComponentConfigs: kubeadmapi.ComponentConfigMap{
+						componentconfigs.KubeletGroup: &componentConfig{},
+					},
+				},
+			},
+		},
+	}
+	for _, tc := range testCases {
+		err := writeKubeletConfigFiles(nil, tc.cfg, tc.patchesDir, tc.dryrun, os.Stdout)
+		if err != nil && tc.errPattern != "" {
+			if match, _ := regexp.MatchString(tc.errPattern, err.Error()); !match {
+				t.Fatalf("Expected error contains %q, got %v", tc.errPattern, err.Error())
+			}
+		}
+		if err == nil && len(tc.errPattern) != 0 {
+			t.Fatalf("writeKubeletConfigFiles didn't return error expected %s", tc.errPattern)
+		}
+	}
+}
+
+// Just some stub code, the code could be enriched when necessary.
+type componentConfig struct {
+	userSupplied bool
+}
+
+func (cc *componentConfig) DeepCopy() kubeadmapi.ComponentConfig {
+	result := &componentConfig{}
+	return result
+}
+
+func (cc *componentConfig) Marshal() ([]byte, error) {
+	return nil, nil
+}
+
+func (cc *componentConfig) Unmarshal(docmap kubeadmapi.DocumentMap) error {
+	return nil
+}
+
+func (cc *componentConfig) Get() interface{} {
+	return &cc
+}
+
+func (cc *componentConfig) Set(cfg interface{}) {
+}
+
+func (cc *componentConfig) Default(_ *kubeadmapi.ClusterConfiguration, _ *kubeadmapi.APIEndpoint, _ *kubeadmapi.NodeRegistrationOptions) {
+}
+
+func (cc *componentConfig) Mutate() error {
+	return nil
+}
+
+func (cc *componentConfig) IsUserSupplied() bool {
+	return false
+}
+func (cc *componentConfig) SetUserSupplied(userSupplied bool) {
+	cc.userSupplied = userSupplied
+}