public function elementShouldBeHidden($selector)
    {
        $session = $this->getSession();
        $page = $session->getPage();
        $element = $page->find('css', $selector);

        if (!$element) {
            throw new ElementNotFoundException($session, 'Element "'.$selector.'"');
        }

        \PHPUnit_Framework_TestCase::assertFalse($element->isVisible());
    }