Symfony2 functional test Unreachable field "_token"

I am creating a functional test in Symfony using the Liip functional test bundle.

I am currently stuck on submiting an form.
I am trying to add a new 'log' using the functional test.

If I try to add a new log trough the UI I get the following request parameters:

'WorkLog' => array(
    'submit' => '',
    'hours' => '8',
    'minutes' => '0',
    'note' => 'some text',
    '_token' => '4l5oPcdCRzxDKKlJt_RG-B1342X52o0C187ZLLVWre4' 
);

But when the test submits the form I get the same parameters but without the token

 'WorkLog' => array(
    'submit' => '',
    'hours' => '8',
    'minutes' => '0',
    'note' => 'some text'
);

I thought I could fix the problem by adding the '_token' field to the form request, but when I ran then test again it gave me an error:

InvalidArgumentException: Unreachable field "_token"

The code of the functional test:

namespace App\AdminBundle\Tests\Controller;

use Liip\FunctionalTestBundle\Test\WebTestCase;

use Symfony\Bundle\FrameworkBundle\Client;
use Symfony\Component\Security\Core\Authentication\Token\UsernamePasswordToken;
use Symfony\Component\BrowserKit\Cookie;

class LogControllerTest extends WebTestCase
{
    private $client;
    private $em;
    private $fixtures;

    public function setUp()
    {
        $this->client = static::makeClient();
        $this->em = $this->client->getContainer()->get('doctrine')->getManager();

        $this->fixtures = $this->loadFixtures(array(
            'App\AdminBundle\DataFixtures\ORM\LoadUserData',
            'App\AdminBundle\DataFixtures\ORM\LoadSubscriptionTypesData',
            'App\AdminBundle\DataFixtures\ORM\LoadSubscriptionData',
            'App\AdminBundle\DataFixtures\ORM\LoadWorkLogData',
        ))->getReferenceRepository();
    }

    public function testAddNewLog()
    {
        $accountId = $this->fixtures->getReference('userAccount')->getId();

        // log in with admin account
        $this->logIn('adminAccount');

        $crawler = $this->client->request('GET', '/admin/worklog/account/'.$accountId.'/add');
        $csrfToken = $this->client->getContainer()->get('form.csrf_provider')->generateCsrfToken('post_type');

        $form = $crawler->selectButton('WorkLog_submit')->form(array(
            'WorkLog' => array(
                'hours' => '8',
                'minutes' => '0',
                'note' => 'some text',
                '_token' => $csrfToken
            ),
        ), 'POST');

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

My question: How can I submit the form with the token?

I don't work with the Liip Functional Test Bundle, but I usually work with form and _token in the following manner:

    $crawler = $this->client->request('GET', $url);

    // retrieves the form token
    $token = $crawler->filter('[name="select_customer[_token]"]')->attr("value");

    // makes the POST request
    $crawler = $this->client->request('POST', $url, array(
        'select_customer' => array(
            '_token' => $token,
            'customerId' => $customerId,
        ),
    ));

Hope this helps.