ManyAssetsTestController.php

<?php

namespace Drupal\many_assets_test\Controller;

use Drupal\Core\Controller\ControllerBase;
class ManyAssetsTestController extends ControllerBase {
    
    /**
     * The render array of the assets testing page.
     *
     * @return array
     */
    public function build() {
        return [
            '#markup' => 'I am a page that tests loading order of many dependencies',
            '#attached' => [
                'library' => [
                    'many_assets_test/weighted',
                    'many_assets_test/many-dependencies',
                    'many_assets_test/weighted_again',
                ],
            ],
        ];
    }

}