t() calls should be avoided in classes, use \Drupal\Core\StringTranslation\StringTranslationTrait and $this->t() instead.
Remove uses of t() in assertions has been done in the issue https://www.drupal.org/project/drupal/issues/3133726.
Remove all calls to t() wrapped in calls to drupalPostForm() will be done in the issue https://www.drupal.org/project/drupal/issues/3145005.
t() calls should be avoided in classes, use $this->t() instead in FeedViewBuilder.php,
DefaultFetcher.php, DefaultParser.php, DefaultProcessor.php, TestProcessor.php, ItemCacheTagsTest.php, ItemWithoutFeedTest.php files.