kubens: Add facility to store state file

Signed-off-by: Ahmet Alp Balkan <ahmetb@google.com>

cmd/kubens/statefile_test.go

@@ -0,0 +1,38 @@
+package main
+
+import (
+	"io/ioutil"
+	"os"
+	"testing"
+)
+
+func TestNSFile(t *testing.T) {
+	td, err := ioutil.TempDir(os.TempDir(), "")
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer os.RemoveAll(td)
+
+	f := NewNSFile("foo")
+	f.dir = td
+	v, err := f.Load()
+	if err != nil {
+		t.Fatal(err)
+	}
+	if v != "" {
+		t.Fatalf("Load() expected empty; got=%v", err)
+	}
+
+	err = f.Save("bar")
+	if err != nil {
+		t.Fatalf("Save() err=%v", err)
+	}
+
+	v, err = f.Load()
+	if err != nil {
+		t.Fatal(err)
+	}
+	if expected := "bar"; v != expected {
+		t.Fatalf("Load()=%q; expected=%q", v, expected)
+	}
+}