isQueued example

    protected function failureDescription($events): string
    {
        return sprintf('the Transport %s (%d %s)', $this->toString(), $this->countNotifications($events), $this->queued ? 'queued' : 'sent');
    }

    private function countNotifications(NotificationEvents $events): int
    {
        $count = 0;
        foreach ($events->getEvents($this->transport) as $event) {
            if (
                ($this->queued && $event->isQueued())
                || (!$this->queued && !$event->isQueued())
            ) {
                ++$count;
            }
        }

        return $count;
    }
}

    public function toString(): string
    {
        return 'is queued';
    }

    /** * @param MessageEvent $event */
    protected function matches($event): bool
    {
        return $event->isQueued();
    }

    /** * @param MessageEvent $event */
    protected function failureDescription($event): string
    {
        return 'the Notification '.$this->toString();
    }
}

    public function toString(): string
    {
        return 'is queued';
    }

    /** * @param MessageEvent $event */
    protected function matches($event): bool
    {
        return $event->isQueued();
    }

    /** * @param MessageEvent $event */
    protected function failureDescription($event): string
    {
        return 'the Email '.$this->toString();
    }
}

    protected function failureDescription($events): string
    {
        return sprintf('the Transport %s (%d %s)', $this->toString(), $this->countEmails($events), $this->queued ? 'queued' : 'sent');
    }

    private function countEmails(MessageEvents $events): int
    {
        $count = 0;
        foreach ($events->getEvents($this->transport) as $event) {
            if (
                ($this->queued && $event->isQueued())
                || (!$this->queued && !$event->isQueued())
            ) {
                ++$count;
            }
        }

        return $count;
    }
}

use Symfony\Component\Mime\Message;

/** * Allows messages to be sent to specific Messenger transports via the "X-Bus-Transport" MIME header. * * @author Fabien Potencier <fabien@symfony.com> */
final class MessengerTransportListener implements EventSubscriberInterface
{
    public function onMessage(MessageEvent $event): void
    {
        if (!$event->isQueued()) {
            return;
        }

        $message = $event->getMessage();
        if (!$message instanceof Message || !$message->getHeaders()->has('X-Bus-Transport')) {
            return;
        }

        $names = $message->getHeaders()->get('X-Bus-Transport')->getBody();
        $names = array_map('trim', explode(',', $names));
        $event->addStamp(new TransportNamesStamp($names));