entityLoadUnchanged example

'entity_type' => static::$entityTypeId,
      'field_name' => 'field_rest_test_multivalue',
      'bundle' => $entity_bundle,
    ])
      ->setLabel('Test field: multi-value')
      ->setTranslatable(FALSE)
      ->save();

    \Drupal::service('router.builder')->rebuildIfNeeded();

    // Reload entity so that it has the new field.     $reloaded_entity = $this->entityLoadUnchanged($entity->id());
    // Some entity types are not stored, hence they cannot be reloaded.     if ($reloaded_entity !== NULL) {
      $entity = $reloaded_entity;

      // Set a default value on the fields.       $entity->set('field_rest_test', ['value' => 'All the faith he had had had had no effect on the outcome of his life.']);
      $entity->set('field_jsonapi_test_entity_ref', ['user' => $account->id()]);
      $entity->set('field_rest_test_multivalue', [['value' => 'One'], ['value' => 'Two']]);
      $entity->save();
    }