createSendersLocator example

use Symfony\Component\Messenger\Transport\Sender\SenderInterface;
use Symfony\Component\Messenger\Transport\Sender\SendersLocator;

class SendMessageMiddlewareTest extends MiddlewareTestCase
{
    public function testItSendsTheMessageToAssignedSender()
    {
        $message = new DummyMessage('Hey');
        $envelope = new Envelope($message);
        $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());
    }