Get dispatched messages with messenger and behat

messenger-behat.php

<?php
      $driver = $this->session->getDriver();
        /** @var Client $client */
        $client = $driver->getClient();
        $nbDispatchedMessages = count($client->getProfile()->getCollector('messenger')->getMessages());
        if ($count !== $nbDispatchedMessages) {
            throw new ExpectationException(
                sprintf('Dispatched messages should be equal to %s, actual : %s', $count, $nbDispatchedMessages),
                $driver
            );
        }