WP_Query Custom Post Type Query by Category Variable

// Shortcode for Custom Post Types [xxx_shortcode category="post-category"]
function xxx_query($atts){
	ob_start();

	$var = shortcode_atts( array(
    	'category' => 'y',
    ), $atts );

    $args = array(
        'post_type'      => 'post',
        'tax_query' => array(array(
        'taxonomy' => 'category',
        'field' => 'slug',
        'terms' => $var['category']))
    );
	
    $query = new WP_Query($args);

    if($query->have_posts()){

        while($query->have_posts()){
            $query->the_post();
        }

    }else{
		echo 'No Posts Available.';
	}
	return ob_get_clean();
}
add_shortcode('xxx_shortcode', 'xxx_query');