my-test-WP_Query

// WP_Query arguments
$args = array(
	'post_type'              => array( 'library_post_type' ),
	'order'                  => 'DESC',
	'orderby'                => 'date',
	'tax_query'              => array(
		array(
			'taxonomy'         => 'library_category',
			'terms'            => 'html-book',
			'field'            => 'slug',
		),
	),
);

// The Query
$query = new WP_Query( $args );