PurgeQueueTestBase: wrote this very thorough base tests which has clean...

PurgeQueueTestBase: wrote this very thorough base tests which has clean derivatives for the Database, File and Memory queue. Although all tests pass perfectly on File and Memory, there's a weird bug in PDO occuring only on the Database plugin, which hasn't been solved yet:

Drupal\Core\Database\DatabaseExceptionWrapper: SQLSTATE[HY000]: General error: failed to instantiate user-supplied statement class: DELETE FROM {queue} WHERE (name = :db_condition_placeholder_0) ; Array ( [:db_condition_placeholder_0] => purge ) in Drupal\Core\Database\Connection->query()