Symfony Unit Test Form Extension Mock

Before updating my code via composer my forms unit test was working. It is now failing on the extension mock. Heres the error:

Argument 1 passed to Symfony\Component\Form\Extension\Validator\Type\FormTypeValidatorExtension::__construct() must be an instance of Symfony\Component\Validator\ValidatorInterface, instance of Mock_ValidatorInterface_14b95ba0 given

Heres my composer required section:

    "require": {
    "php": ">=5.3.3",
    "symfony/symfony": "~2.3",
    "doctrine/orm": "~2.2,>=2.2.3",
    "doctrine/doctrine-bundle": "~1.2",
    "twig/extensions": "~1.0",
    "symfony/assetic-bundle": "~2.3",
    "symfony/swiftmailer-bundle": "~2.3",
    "symfony/monolog-bundle": "~2.3",
    "symfony/monolog-bridge": "~2.4",
    "sensio/distribution-bundle": "~2.3",
    "sensio/framework-extra-bundle": "~2.3"
   }

Heres the validation mock in the unit test setup method:

use Symfony\Component\Form\Test\TypeTestCase;
use Symfony\Component\Form\Forms;
use Symfony\Component\Form\FormBuilder;
use Symfony\Component\Form\Extension\Validator\Type\FormTypeValidatorExtension;
use Symfony\Component\Validator\ConstraintViolationList;
use Symfony\Component\Form\Extension\Core\CoreExtension;

class TestedTypeTest extends TypeTestCase
{

protected function setUp()
{
    parent::setUp();

    $validator = $this->getMock('\Symfony\Component\Validator\Validator\ValidatorInterface');
    $validator->method('validate')->will($this->returnValue(new ConstraintViolationList()));
    $formTypeExtension = new FormTypeValidatorExtension($validator);
    $coreExtension = new CoreExtension();

    $this->factory = Forms::createFormFactoryBuilder()
            ->addExtensions($this->getExtensions())
            ->addExtension($coreExtension)
            ->addTypeExtension($formTypeExtension)
            ->getFormFactory();
}

Does anyone know what might be wrong with the mock? Any advice is greatly appreciated.