getSenderAlias example

    public function reject(Envelope $envelope): void
    {
        throw new InvalidArgumentException('You cannot call reject() on the Messenger SyncTransport.');
    }

    public function send(Envelope $envelope): Envelope
    {
        /** @var SentStamp|null $sentStamp */
        $sentStamp = $envelope->last(SentStamp::class);
        $alias = null === $sentStamp ? 'sync' : ($sentStamp->getSenderAlias() ?: $sentStamp->getSenderClass());

        $envelope = $envelope->with(new ReceivedStamp($alias));

        return $this->messageBus->dispatch($envelope);
    }
}

$sender = $this->createMock(SenderInterface::class);

        $sendersLocator = $this->createSendersLocator([DummyMessage::class => ['my_sender']], ['my_sender' => $sender]);
        $middleware = new SendMessageMiddleware($sendersLocator);

        $sender->expects($this->once())->method('send')->with($envelope->with(new SentStamp($sender::class, 'my_sender')))->willReturnArgument(0);

        $envelope = $middleware->handle($envelope, $this->getStackMock(false));

        /* @var SentStamp $stamp */
        $this->assertInstanceOf(SentStamp::class, $stamp = $envelope->last(SentStamp::class), 'it adds a sent stamp');
        $this->assertSame('my_sender', $stamp->getSenderAlias());
        $this->assertStringMatchesFormat('Mock_SenderInterface_%s', $stamp->getSenderClass());
    }

    public function testItSendsTheMessageToMultipleSenders()
    {
        $envelope = new Envelope(new DummyMessage('Hey'));
        $sender = $this->createMock(SenderInterface::class);
        $sender2 = $this->createMock(SenderInterface::class);

        $sendersLocator = $this->createSendersLocator([DummyMessage::class => ['foo', 'bar']], ['foo' => $sender, 'bar' => $sender2]);
        $middleware = new SendMessageMiddleware($sendersLocator);