Issue #3284759 by longwave: Remove deprecated BcTimestampNormalizerUnixTestTrait

<?php

namespace Drupal\Tests\rest\Functional;

@trigger_error(__NAMESPACE__ . '\BcTimestampNormalizerUnixTestTrait is deprecated in Drupal 9.0.0 and will be removed before Drupal 10.0.0. Instead of BcTimestampNormalizerUnixTestTrait::formatExpectedTimestampItemValues(123456789), use (new \DateTime())->setTimestamp(123456789)->setTimezone(new \DateTimeZone("UTC"))->format(\DateTime::RFC3339), see https://www.drupal.org/node/2859657.', E_USER_DEPRECATED);

/**

 * Trait for ResourceTestBase subclasses formatting expected timestamp data.

 */

trait BcTimestampNormalizerUnixTestTrait {

  /**

   * Formats a UNIX timestamp.

   *

   * @param int $timestamp

   *   The timestamp value to format.

   *

   * @return string

   *   The formatted RFC3339 date string.

   *

   * @see \Drupal\serialization\Normalizer\TimestampItemNormalizer

   */

  protected function formatExpectedTimestampItemValues($timestamp) {

    $date = new \DateTime();

    $date->setTimestamp($timestamp);

    // Per \Drupal\Core\TypedData\Plugin\DataType\Timestamp::getDateTime(), they

    // default to string representations in the UTC timezone.

    $date->setTimezone(new \DateTimeZone('UTC'));

    // Format is also added to the expected return values.

    return [

      'value' => $date->format(\DateTime::RFC3339),

      'format' => \DateTime::RFC3339,

    ];

  }

}