test?

ok

// Register Default Headers
function custom_default_headers() {

	$headers = array(
		'test' => array(
			'description'   => __( 'test', 'text_domain' ),
			'url'           => '',
			'thumbnail_url' => '',
		),
	);
	register_default_headers( $headers );

}
add_action( 'after_setup_theme', 'custom_default_headers' );