wp-cli command for testing https://core.trac.wordpress.org/ticket/30261

wp-cli-bbg.php

<?php

// Bail if WP-CLI is not present.
if ( !defined( 'WP_CLI' ) ) return;

class BBG_Command extends WP_CLI_Command {

	public function generate_shared_terms( $args, $assoc_args ) {
		global $wpdb;

		$defaults = array(
			'count' => 10,
			'from_taxonomy' => 'post_tag',
			'to_taxonomy' => 'category',
		);

		$r = array_merge( $defaults, $assoc_args );

		// Create some base terms in the 'category' taxonomy.
		$_args = array( 'term', 'generate', 'category' );
		$_assoc_args = array( 'count' => $r['count'], 'max_depth' => 4 );
		WP_CLI::run_command( $_args, $_assoc_args );

		// Get the IDs of the terms just created.
		$source_term_ids = $wpdb->get_col( "SELECT * FROM $wpdb->terms ORDER BY term_id DESC limit " . intval( $r['count'] ) );

		$c = array(
			'foo1' => array( 'start' => $source_term_ids[0], 'count' => floor( $r['count'] / 2 ) ),
			'foo2' => array( 'start' => $source_term_ids[0], 'count' => $r['count'] - 1 ),
			'foo3' => array( 'start' => $source_term_ids[0], 'count' => floor( $r['count'] / 3 ) ),
			'foo4' => array( 'start' => $source_term_ids[0], 'count' => floor( $r['count'] / 2 ) ),
		);

		foreach ( $c as $ctax => $cdata ) {
			register_taxonomy( $ctax, 'post' );
			$to_tax_obj = get_taxonomy( $ctax );
			$label = $to_tax_obj->labels->singular_name;
			$notify = \WP_CLI\Utils\make_progress_bar( 'Generating shared terms in taxonomy ' . $ctax, $r['count'] );

			for ( $i = $cdata['start']; $i < ( $cdata['start'] + $cdata['count'] ); $i++ ) {
				// Create a new term.
				$term = wp_insert_term( $label . ' ' . rand( 0, 9999999 ), $ctax );

				if ( is_wp_error( $term ) ) {
					WP_CLI::warning( $term );
				} else {
					$wpdb->update( $wpdb->term_taxonomy,
						array( 'term_id' => $i ),
						array( 'term_taxonomy_id' => $term['term_taxonomy_id'] )
					);
				}

				$notify->tick();
			}

			$notify->finish();
		}

	}
}

WP_CLI::add_command( 'bbg', 'BBG_Command' );