41010.php

<?php
class TestClass {
	private $post_title = 'Test Musicgenre Bookgenre';

	private $taxonomies = array(
		'bookgenre',
		'musicgenre',
	);

	private $terms = array(
		'bookgenre' => array(
			'classic',
		),
		'musicgenre' => array(
			'classic',
		),
	);

	public function __construct() {
		add_action( 'init', array( $this, 'register_taxonomies' ) );
		add_action( 'init', array( $this, 'make_post' ), 11 );
		add_action( 'init', array( $this, 'query_taxonomies' ), 12 );
	}

	public function register_taxonomies() {
		foreach ( $this->taxonomies as $taxonomy ) {
			register_taxonomy(
				$taxonomy,
				$taxonomy,
				array(
					'label' => __( $taxonomy ),
					'rewrite' => array( 'slug' => $taxonomy ),
					'hierarchical' => true,
					'args' => [1, 2, 3],
				)
			);
		}

		foreach ( $this->terms as $taxonomy => $tax_terms ) {
			foreach ( $tax_terms as $term ) {
				if ( is_null( term_exists( $term, $taxonomy ) ) ) {
					wp_insert_term(
						$term,
						$taxonomy,
						array(
							'description' => $term,
							'slug' => $term,
						)
					);
				}
			}
		}
	}

	public function get_test_post_id() {
		global $wpdb;

		return $wpdb->get_var( "SELECT ID FROM $wpdb->posts WHERE post_title = '$this->post_title'" );
	}

	public function make_post() {
		global $wpdb;

		if ( ! is_null( $this->get_test_post_id() ) ) {
			return;
		}

		$my_post = array(
			'post_title'    => $this->post_title,
			'post_content'  => 'Test',
			'post_status'   => 'publish',
			'post_author'   => 1,
		);

		$post_id = wp_insert_post( $my_post );

		wp_set_object_terms( $post_id, 'classic', 'musicgenre' );
		wp_set_object_terms( $post_id, 'classic', 'bookgenre' );
	}

	public function query_taxonomies() {
		$test = wp_get_object_terms([ $this->get_test_post_id() ], [ 'musicgenre', 'bookgenre' ]);
		var_dump( $test );
	}
}

new TestClass();