Merge pull request #43514 from zjj2wry/006

Automatic merge from submit-queue (batch tested with PRs 44047, 43514, 44037, 43467)

unit test for kubectl config use-context

**What this PR does / why we need it**:
unit test for kubectl config use-context

**Which issue this PR fixes** *(optional, in `fixes #<issue number>(, fixes #<issue_number>, ...)` format, will close that issue when PR gets merged)*: fixes #

**Special notes for your reviewer**:
think you

**Release note**:

```release-note
```

pkg/kubectl/cmd/config/BUILD

@@ -57,6 +57,7 @@ go_test(
         "get_contexts_test.go",
         "navigation_step_parser_test.go",
         "unset_test.go",
+        "use_context_test.go",
     ],
     library = ":go_default_library",
     tags = ["automanaged"],

pkg/kubectl/cmd/config/use_context_test.go

@@ -0,0 +1,104 @@
+/*
+Copyright 2017 The Kubernetes Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package config
+
+import (
+	"bytes"
+	"io/ioutil"
+	"os"
+	"testing"
+
+	"k8s.io/client-go/tools/clientcmd"
+	clientcmdapi "k8s.io/client-go/tools/clientcmd/api"
+)
+
+type useContextTest struct {
+	description    string
+	config         clientcmdapi.Config //initiate kubectl config
+	args           []string            //kubectl config use-context args
+	expected       string              //expect out
+	expectedConfig clientcmdapi.Config //expect kubectl config
+}
+
+func TestUseContext(t *testing.T) {
+	conf := clientcmdapi.Config{
+		Kind:       "Config",
+		APIVersion: "v1",
+		Clusters: map[string]*clientcmdapi.Cluster{
+			"minikube":   {Server: "https://192.168.99.100:8443"},
+			"my-cluster": {Server: "https://192.168.0.1:3434"},
+		},
+		Contexts: map[string]*clientcmdapi.Context{
+			"minikube":   {AuthInfo: "minikube", Cluster: "minikube"},
+			"my-cluster": {AuthInfo: "mu-cluster", Cluster: "my-cluster"},
+		},
+		CurrentContext: "minikube",
+	}
+	test := useContextTest{
+		description: "Testing for kubectl config use-context",
+		config:      conf,
+		args:        []string{"my-cluster"},
+		expected:    `Switched to context "my-cluster".` + "\n",
+		expectedConfig: clientcmdapi.Config{
+			Kind:       "Config",
+			APIVersion: "v1",
+			Clusters: map[string]*clientcmdapi.Cluster{
+				"minikube":   {Server: "https://192.168.99.100:8443"},
+				"my-cluster": {Server: "https://192.168.0.1:3434"},
+			},
+			Contexts: map[string]*clientcmdapi.Context{
+				"minikube":   {AuthInfo: "minikube", Cluster: "minikube"},
+				"my-cluster": {AuthInfo: "mu-cluster", Cluster: "my-cluster"},
+			},
+			CurrentContext: "my-cluster",
+		},
+	}
+	test.run(t)
+}
+
+func (test useContextTest) run(t *testing.T) {
+	fakeKubeFile, err := ioutil.TempFile(os.TempDir(), "")
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	defer os.Remove(fakeKubeFile.Name())
+	err = clientcmd.WriteToFile(test.config, fakeKubeFile.Name())
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	pathOptions := clientcmd.NewDefaultPathOptions()
+	pathOptions.GlobalFile = fakeKubeFile.Name()
+	pathOptions.EnvVar = ""
+	buf := bytes.NewBuffer([]byte{})
+	cmd := NewCmdConfigUseContext(buf, pathOptions)
+	cmd.SetArgs(test.args)
+	if err := cmd.Execute(); err != nil {
+		t.Fatalf("unexpected error executing command: %v,kubectl config use-context args: %v", err, test.args)
+	}
+	config, err := clientcmd.LoadFromFile(fakeKubeFile.Name())
+	if err != nil {
+		t.Fatalf("unexpected error loading kubeconfig file: %v", err)
+	}
+	if len(test.expected) != 0 {
+		if buf.String() != test.expected {
+			t.Errorf("Failed in :%q\n expected %v\n, but got %v\n", test.description, test.expected, buf.String())
+		}
+	}
+	if test.expectedConfig.CurrentContext != config.CurrentContext {
+		t.Errorf("Failed in :%q\n expected config %v, but found %v\n in kubeconfig\n", test.description, test.expectedConfig, config)
+	}
+}