fail properly when the required service is not defined

Author: xabbuh

Test/MailerAssertionsTrait.php

@@ -122,10 +122,10 @@ private static function getMessageMailerEvents(): MessageEvents
             static::fail('Unable to make email assertions. Did you forget to make an HTTP request?');
         }
 
-        if (!$logger = self::$container->get('mailer.logger_message_listener')) {
+        if (!self::$container->has('mailer.logger_message_listener')) {
             static::fail('A client must have Mailer enabled to make email assertions. Did you forget to require symfony/mailer?');
         }
 
-        return $logger->getEvents();
+        return self::$container->get('mailer.logger_message_listener')->getEvents();
     }
 }