[Notifier] Replace tests dummy instances by already in place mocks

Author: alexandre-daubois

Tests/LinkedInTransportTest.php

@@ -16,13 +16,11 @@
 use Symfony\Component\Notifier\Exception\LogicException;
 use Symfony\Component\Notifier\Exception\TransportException;
 use Symfony\Component\Notifier\Message\ChatMessage;
-use Symfony\Component\Notifier\Message\MessageInterface;
 use Symfony\Component\Notifier\Message\MessageOptionsInterface;
 use Symfony\Component\Notifier\Message\SmsMessage;
 use Symfony\Component\Notifier\Notification\Notification;
 use Symfony\Component\Notifier\Test\TransportTestCase;
-use Symfony\Component\Notifier\Tests\Fixtures\DummyHttpClient;
-use Symfony\Component\Notifier\Tests\Fixtures\DummyMessage;
+use Symfony\Component\Notifier\Tests\Transport\DummyMessage;
 use Symfony\Component\Notifier\Transport\TransportInterface;
 use Symfony\Contracts\HttpClient\HttpClientInterface;
 use Symfony\Contracts\HttpClient\ResponseInterface;
@@ -34,7 +32,7 @@ final class LinkedInTransportTest extends TransportTestCase
      */
     public static function createTransport(HttpClientInterface $client = null): TransportInterface
     {
-        return (new LinkedInTransport('AuthToken', 'AccountId', $client ?? new DummyHttpClient()))->setHost('host.test');
+        return (new LinkedInTransport('AuthToken', 'AccountId', $client ?? new MockHttpClient()))->setHost('host.test');
     }
 
     public static function toStringProvider(): iterable