assetic and functional testing

[Elexy]

Trying to test a Symfony2 page that runs fine in the browser (dev and prod)
When trying to run functional tests like described in the manual i get:

string(49618) " An exception has been thrown during the rendering of a template ("Rou te "_assetic_2875553_0" does not exist.") in "ProjectXFrontendBundle::layout.html.twig" at line 6. (500 Internal Server Error)

The number is correct, but the generated files are called:
2875553_part_1_base_1 etc...

I'm using SF 2.0.12

Any ideas anyone?

test code:

public function testIndex()
   {
      $client = static::createClient();

      $crawler = $client->request('GET', '/');
      var_dump($crawler->text()); //debug
      $this->assertTrue($crawler->filter('html:contains("Benefits")')->count() > 0, "assert text <benefits>");
      $this->assertTrue($crawler->filter('a:contains("Login")')->count() > 0, "Login found on page");
      $link = $crawler->selectLink("Login")->link();
      $this->assertTrue((bool) $link);
      $crawler = $client->click($link);
      $this->assertTrue($crawler->filter('html:contains("Remember me")')->count() > 0);
   }