icon from select option BY Meta Box

// if user want to select icon from select option

$meta_boxes['test_metabox'] = array(
        'id'         => 'test_metabox',
        'title'      => __( 'Font Awesome', 'cmb' ),
        'pages'      => array( 'acme_product', ), // Post type
        'context'    => 'normal',
        'priority'   => 'high',
        'show_names' => true, // Show field names on the left
        // 'cmb_styles' => true, // Enqueue the CMB stylesheet on the frontend
        'fields'     => array(
            array(
                'name'       => __( 'Font Awesome', 'cmb' ),
                'desc'       => __( 'write your icon name', 'cmb' ),
                'id'         =>'promo-icon',
                'type'       => 'select',
                'show_on_cb' => 'cmb_test_text_show_on_cb', // function should return a bool value
                // 'sanitization_cb' => 'my_custom_sanitization', // custom sanitization callback parameter
                // 'escape_cb'       => 'my_custom_escaping',  // custom escaping callback parameter
                // 'on_front'        => false, // Optionally designate a field to wp-admin only
                // 'repeatable'      => true,
                'options' => array(
                    'Home' => __( 'Home Icon', 'cmb' ),
                    'facebook'   => __( 'Facebook Icon', 'cmb' ),
                    'Twitter'     => __( 'Twitter Icon', 'cmb' ),
                    'search'     => __( 'Search Icon', 'cmb' ),
                ),
            ),