diff --git a/legacy/elementary/src/bin/test_radio.c b/legacy/elementary/src/bin/test_radio.c
index 28187ef38c..2c1a8b6cc4 100644
--- a/legacy/elementary/src/bin/test_radio.c
+++ b/legacy/elementary/src/bin/test_radio.c
@@ -10,6 +10,13 @@ _rd_changed_cb(void *data EINA_UNUSED, Evas_Object *obj,
    printf("radio value : %d\n", elm_radio_value_get(obj));
 }
 
+static void
+_rdg_changed_cb(void *data EINA_UNUSED, Evas_Object *obj,
+                void *event_info EINA_UNUSED)
+{
+   printf("radio group value : %d\n", elm_radio_value_get(obj));
+}
+
 void
 test_radio(void *data EINA_UNUSED, Evas_Object *obj EINA_UNUSED,
            void *event_info EINA_UNUSED)
@@ -40,7 +47,10 @@ test_radio(void *data EINA_UNUSED, Evas_Object *obj EINA_UNUSED,
    elm_box_pack_end(bx, rd);
    evas_object_show(rd);
    evas_object_smart_callback_add(rd, "changed", _rd_changed_cb, NULL);
+
+   // rdg radio group
    rdg = rd;
+   evas_object_smart_callback_add(rdg, "changed", _rdg_changed_cb, NULL);
 
    ic = elm_icon_add(win);
    snprintf(buf, sizeof(buf), "%s/images/logo_small.png", elm_app_data_dir_get());
@@ -58,7 +68,7 @@ test_radio(void *data EINA_UNUSED, Evas_Object *obj EINA_UNUSED,
 
    rd = elm_radio_add(win);
    elm_radio_state_value_set(rd, 2);
-   elm_radio_group_add(rd, rdg);
+   elm_radio_group_add(rd, rdg); // add a radio button rd to a radio group rdg.
    elm_object_text_set(rd, "Label Only");
    elm_box_pack_end(bx, rd);
    evas_object_show(rd);
@@ -66,7 +76,7 @@ test_radio(void *data EINA_UNUSED, Evas_Object *obj EINA_UNUSED,
 
    rd = elm_radio_add(win);
    elm_radio_state_value_set(rd, 3);
-   elm_radio_group_add(rd, rdg);
+   elm_radio_group_add(rd, rdg); // add a radio button rd to a radio group rdg.
    elm_object_text_set(rd, "Disabled");
    elm_object_disabled_set(rd, EINA_TRUE);
    elm_box_pack_end(bx, rd);
@@ -80,7 +90,7 @@ test_radio(void *data EINA_UNUSED, Evas_Object *obj EINA_UNUSED,
 
    rd = elm_radio_add(win);
    elm_radio_state_value_set(rd, 4);
-   elm_radio_group_add(rd, rdg);
+   elm_radio_group_add(rd, rdg); // add a radio button rd to a radio group rdg.
    elm_object_part_content_set(rd, "icon", ic);
    elm_box_pack_end(bx, rd);
    evas_object_show(rd);
@@ -93,7 +103,7 @@ test_radio(void *data EINA_UNUSED, Evas_Object *obj EINA_UNUSED,
 
    rd = elm_radio_add(win);
    elm_radio_state_value_set(rd, 5);
-   elm_radio_group_add(rd, rdg);
+   elm_radio_group_add(rd, rdg); // add a radio button rd to a radio group rdg.
    elm_object_part_content_set(rd, "icon", ic);
    elm_object_disabled_set(rd, EINA_TRUE);
    elm_box_pack_end(bx, rd);