Maximum function nesting level of '100' reached while testing my Guzzle client?

My very basic understanding of Guzzle internals maybe the cause of this error (PHPUnit test):

PHP Fatal error: Maximum function nesting level of '100' reached, aborting! in \vendor\guzzle\guzzle\src\Guzzle\Http\QueryString.php on line 234

It seems that the following sections (plugin and parser) are calling each other. The plugin is listening for command.before_send event, adding a closure as listener for the request.exception event:

/**
 * The plugin adds a closure listener for the event 'response.exception'. The
 * closure is using the parser (RestInterfaceParser).
 */
class ResponseListener implements EventSubscriberInterface
{
    public static function getSubscribedEvents()
    {
        return array('command.before_send' => 'onCommandBeforeSend');
    }

    public function onCommandBeforeSend(Event $event)
    {
        // ...
        $command = $event['command'];
        $request = $command->getRequest();

        $request->getEventDispatcher()->addListener(
            'request.exception',
            function (Event $event) use ($command, $parser) {
                $parsed = $parser->parse($command);

                // ...
            }
        );
    }
}

Nothing special so far! The error is caused by the parser, when I try to access the response object:

/**
 * The parser invoked by the closure listener.
 */
class RestInterfaceParser implements ResponseParserInterface
{
    public function parse(CommandInterface $command)
    {
        var_dump($command->getResponse());
    }
}

Removing that line removes the error. But, big surprise, I need the response object inside the parser. Increasing the nesting level (xdebug.max_nesting_level = 1000) doesn't help because it's "pure" recursion here.