Fix handling for KUBECONFIG env var (#192)

* Fix handling for KUBECONFIG env var

* Address comments

cmd/root.go

@@ -31,11 +31,10 @@ import (
 )
 
 var (
-	defaultKubeCfg = ""
-	kubecfg        string
-	dryrun         bool
-	timeout        time.Duration
-	logLevel       = "info"
+	kubecfg  string
+	dryrun   bool
+	timeout  time.Duration
+	logLevel = "info"
 
 	rootCmd = &cobra.Command{
 		Use:   "kne",
@@ -62,12 +61,19 @@ func ExecuteContext(ctx context.Context) error {
 	return rootCmd.ExecuteContext(ctx)
 }
 
-func init() {
+func defaultKubeCfg() string {
+	if v := os.Getenv("KUBECONFIG"); v != "" {
+		return v
+	}
 	if home := homedir.HomeDir(); home != "" {
-		defaultKubeCfg = filepath.Join(home, ".kube", "config")
+		return filepath.Join(home, ".kube", "config")
 	}
+	return ""
+}
+
+func init() {
 	rootCmd.SetOut(os.Stdout)
-	rootCmd.PersistentFlags().StringVar(&kubecfg, "kubecfg", defaultKubeCfg, "kubeconfig file")
+	rootCmd.PersistentFlags().StringVar(&kubecfg, "kubecfg", defaultKubeCfg(), "kubeconfig file")
 	rootCmd.PersistentFlags().StringVarP(&logLevel, "verbosity", "v", logLevel, "log level")
 	createCmd.Flags().BoolVar(&dryrun, "dryrun", false, "Generate topology but do not push to k8s")
 	createCmd.Flags().DurationVar(&timeout, "timeout", 0, "Timeout for pod status enquiry")

cmd/root_test.go

@@ -0,0 +1,57 @@
+package cmd
+
+import (
+	"os"
+	"testing"
+)
+
+func TestGetKubeCfg(t *testing.T) {
+	tests := []struct {
+		desc   string
+		setVar func() func()
+		want   string
+	}{{
+		desc: "KUBECONFIG Set",
+		setVar: func() func() {
+			orig := os.Getenv("KUBECONFIG")
+			os.Setenv("KUBECONFIG", "/etc/kube/config")
+			return func() {
+				os.Setenv("KUBECONFIG", orig)
+			}
+		},
+		want: "/etc/kube/config",
+	}, {
+		desc: "home dir",
+		setVar: func() func() {
+			orig := os.Getenv("HOME")
+			os.Setenv("HOME", "/fakeuser")
+			return func() {
+				os.Setenv("HOME", orig)
+			}
+		},
+		want: "/fakeuser/.kube/config",
+	}, {
+		desc: "unknown",
+		setVar: func() func() {
+			origH := os.Getenv("HOME")
+			os.Setenv("HOME", "")
+			origK := os.Getenv("KUBECONFIG")
+			os.Setenv("KUBECONFIG", "")
+			return func() {
+				os.Setenv("HOME", origH)
+				os.Setenv("KUBECONFIG", origK)
+			}
+		},
+		want: "",
+	}}
+	for _, tt := range tests {
+		t.Run(tt.desc, func(t *testing.T) {
+			unset := tt.setVar()
+			defer unset()
+			got := defaultKubeCfg()
+			if got != tt.want {
+				t.Fatalf("getKubeCfg() failed: got %v, want %v", got, tt.want)
+			}
+		})
+	}
+}