test 1

// WP_Query arguments
$args = array(
	'post_type'              => array( 'store' ),
	'nopaging'               => true,
	'posts_per_page'         => '4',
	'order'                  => 'DESC',
	'orderby'                => 'title',
	'tax_query'              => array(
		'relation' => 'AND',
		array(
			'taxonomy'         => 'author',
			'terms'            => '21',
			'field'            => 'term_id',
			'operator'         => 'IN',
			'include_children' => true,
		),
	),
);

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

// The Loop
if ( $store->have_posts() ) {
	while ( $store->have_posts() ) {
		$store->the_post();
		// do something
	}
} else {
	// no posts found
}

// Restore original Post Data
wp_reset_postdata();