kubeadm: add better test coverage to version.go

add the following tests in the new file
version_test.go:

- TestNewCmdVersion()
- TestRunVersion()

cmd/kubeadm/app/cmd/BUILD

@@ -82,12 +82,14 @@ go_test(
     srcs = [
         "reset_test.go",
         "token_test.go",
+        "version_test.go",
     ],
     embed = [":go_default_library"],
     deps = [
         "//cmd/kubeadm/app/apis/kubeadm/v1alpha1:go_default_library",
         "//cmd/kubeadm/app/constants:go_default_library",
         "//cmd/kubeadm/app/preflight:go_default_library",
+        "//vendor/github.com/ghodss/yaml:go_default_library",
         "//vendor/k8s.io/api/core/v1:go_default_library",
         "//vendor/k8s.io/apimachinery/pkg/api/errors:go_default_library",
         "//vendor/k8s.io/apimachinery/pkg/apis/meta/v1:go_default_library",

cmd/kubeadm/app/cmd/version_test.go

@@ -0,0 +1,96 @@
+/*
+Copyright 2018 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 cmd
+
+import (
+	"bytes"
+	"encoding/json"
+	"fmt"
+	"github.com/ghodss/yaml"
+	"testing"
+)
+
+func TestNewCmdVersion(t *testing.T) {
+	var buf bytes.Buffer
+	cmd := NewCmdVersion(&buf)
+	if err := cmd.Execute(); err != nil {
+		t.Errorf("Cannot execute version command: %v", err)
+	}
+}
+
+func TestRunVersion(t *testing.T) {
+	var buf bytes.Buffer
+	iface := make(map[string]interface{})
+	flagNameOutput := "output"
+	cmd := NewCmdVersion(&buf)
+
+	testCases := []struct {
+		name              string
+		flag              string
+		expectedError     bool
+		shouldBeValidYAML bool
+		shouldBeValidJSON bool
+	}{
+		{
+			name: "valid: run without flags",
+		},
+		{
+			name: "valid: run with flag 'short'",
+			flag: "short",
+		},
+		{
+			name:              "valid: run with flag 'yaml'",
+			flag:              "yaml",
+			shouldBeValidYAML: true,
+		},
+		{
+			name:              "valid: run with flag 'json'",
+			flag:              "json",
+			shouldBeValidJSON: true,
+		},
+		{
+			name:          "invalid: run with unsupported flag",
+			flag:          "unsupported-flag",
+			expectedError: true,
+		},
+	}
+	for _, tc := range testCases {
+		var err error
+		if len(tc.flag) > 0 {
+			if err = cmd.Flags().Set(flagNameOutput, tc.flag); err != nil {
+				goto error
+			}
+		}
+		buf.Reset()
+		if err = RunVersion(&buf, cmd); err != nil {
+			goto error
+		}
+		if buf.String() == "" {
+			err = fmt.Errorf("empty output")
+			goto error
+		}
+		if tc.shouldBeValidYAML {
+			err = yaml.Unmarshal(buf.Bytes(), &iface)
+		} else if tc.shouldBeValidJSON {
+			err = json.Unmarshal(buf.Bytes(), &iface)
+		}
+	error:
+		if (err != nil) != tc.expectedError {
+			t.Errorf("Test case %q: RunVersion expected error: %v, saw: %v; %v", tc.name, tc.expectedError, err != nil, err)
+		}
+	}
+}