BTB_shutdown_workaround.php

<?php

class myTest extends BrowserTestBase {

  /**
   * @{@inheritdoc}
   */
  protected function tearDown() {
    if (function_exists('_drupal_shutdown_function')) {
      _drupal_shutdown_function();
      $callback = &drupal_register_shutdown_function();
      $callback = [];
    }
    parent::tearDown();
  }
}