I have a functional test that does this :

$form = $crawler->selectButton('Submit the form')->form(array(
    'project[title]' => 'Foo',
    'project[summary]' => 'Bar'
));
$form['project[pictureFile]']->upload('some/file.png');
$this->client->submit($form);

It used to work on 2.4 but no more on 2.5 :

Cannot access  property Symfony\Component\Validator\Constraints\ImageValidator::$suffices in Symfony/Component/Validator/Constraints/FileValidator.php on line 163

The problem is introduced by e4c6da5. I guess it's because we use static::$attribute from an inherited class on a private property in FileValidator.php:163.