Issue #3069050 by voleger, mikelutz: Properly deprecate FormattedDateDiff::getMaxAge()

   * @return int

   *   The maximum time in seconds that this object may be cached.

   *

   * @deprecated in Drupal 8.1.9 and will be removed before Drupal 9.0.0. Use

   * @deprecated in drupal:8.1.9 and is removed from drupal:9.0.0. Use

   *   \Drupal\Core\Datetime\FormattedDateDiff::getCacheMaxAge() instead.

   *

   * @see https://www.drupal.org/node/2783545

   */

  public function getMaxAge() {

    @trigger_error(__NAMESPACE__ . '\FormattedDateDiff::getMaxAge() is deprecated in drupal:8.1.9 and is removed from drupal:9.0.0. Use \Drupal\Core\Datetime\FormattedDateDiff::getCacheMaxAge() instead. See https://www.drupal.org/node/2783545', E_USER_DEPRECATED);

    return $this->getCacheMaxAge();

  }

    $build = [];

    CacheableMetadata::createFromObject($object)->applyTo($build);

    $this->assertEquals($max_age, $build['#cache']['max-age']);

    // Test the BC layer.

  }

  /**

   * Tests FormattedDateDiff.

   *

   * @covers \Drupal\Core\Datetime\FormattedDateDiff::getMaxAge

   * @group legacy

   * @expectedDeprecation Drupal\Core\Datetime\FormattedDateDiff::getMaxAge() is deprecated in drupal:8.1.9 and is removed from drupal:9.0.0. Use \Drupal\Core\Datetime\FormattedDateDiff::getCacheMaxAge() instead. See https://www.drupal.org/node/2783545

   */

  public function testLegacyMaxAgeFormattedDateDiff() {

    $string = '10 minutes';

    $max_age = 60;

    $object = new FormattedDateDiff($string, $max_age);

    $this->assertSame($object->getCacheMaxAge(), $object->getMaxAge());

  }