address lavalamp's comment on using testapi instead of latest, and adding comments for public method.

pkg/api/install/install_test.go

@@ -46,6 +46,8 @@ func TestResourceVersioner(t *testing.T) {
 
 func TestCodec(t *testing.T) {
 	pod := internal.Pod{}
+	// We do want to use package latest rather than testapi here, because we
+	// want to test if the package install and package latest work as expected.
 	data, err := latest.GroupOrDie("").Codec.Encode(&pod)
 	if err != nil {
 		t.Fatalf("unexpected error: %v", err)