DummyBatchHandler example

        $expectedMessages = [
            new DummyMessage('Hey'),
            new DummyMessage('Bob'),
        ];

        $receiver = new DummyReceiver([
            [new Envelope($expectedMessages[0])],
            [new Envelope($expectedMessages[1])],
        ]);

        $handler = new DummyBatchHandler();

        $middleware = new HandleMessageMiddleware(new HandlersLocator([
            DummyMessage::class => [new HandlerDescriptor($handler)],
        ]));

        $bus = new MessageBus([$middleware]);

        $dispatcher = new EventDispatcher();
        $dispatcher->addListener(WorkerRunningEvent::class, function DWorkerRunningEvent $event) use ($receiver) {
            static $i = 0;
            if (1 < ++$i) {