Test in sonata admin bundle

I'm trying to verify that a form with children objects works in sonata admin bundle.

The problem is that the form I want to check has associated children objects.

$form = $crawler->selectButton('Crear y editar')->form(array());
parse_str(parse_url($form->getFormNode()->getAttribute('action'))['query']);
  $form["{$uniqid}[fechaEmision]"]->setValue('31/05/2018');

$crawler = $this->client->submit($form);

The problem radiates that I can not add new elements.