$slack = new Symfony\Component\Notifier\Bridge\Slack\SlackTransport('xoxb-some-token', 'some-channel');
    $opts = new \Symfony\Component\Notifier\Bridge\Slack\SlackOptions(['unfurl_links' => false]);
    $message = new \Symfony\Component\Notifier\Message\ChatMessage('Test message with a link to https://www.github.com/', $opts);
    $slack->send($message);

array(3) {
  ["unfurl_links"]=>
  bool(false)
  ["channel"]=>
  string(17) "some-channel"
  ["text"]=>
  string(35) "Test message with a link to https://www.github.com/'"
}
array(3) {
  ["channel"]=>
  string(17) "some-channel"
  ["text"]=>
  string(35) "Test message with a link to https://www.github.com/'"
}