ClassFilterSubscriber.php

<?php

namespace Drupal\ilr_registrations\EventSubscriber;

use Symfony\Component\EventDispatcher\EventSubscriberInterface;
use Symfony\Component\EventDispatcher\Event;
use Drupal\commerce_product\Event\ProductEvents;
use Drupal\commerce_product\Event\FilterVariationsEvent;

/**
 * Class ClassFilterSubscriber.
 */
class ClassFilterSubscriber implements EventSubscriberInterface {


  /**
   * Constructs a new ClassFilterSubscriber object.
   */
  public function __construct() {

  }

  /**
   * {@inheritdoc}
   */
  static function getSubscribedEvents() {
    $events[ProductEvents::FILTER_VARIATIONS] = 'onClassFilter';
    return $events;
  }

  /**
   * Code to run before a migration has been imported.
   */
    public function onClassFilter(FilterVariationsEvent $event) {
      dump($event);
      // foreach ($event['#variations'] as $variation) {
      //   dump($variation);
      // }

    }
}