PHPUnit Image:make cause a problem

Hi, I have a problem doing my PHPUnit tests. This line:

Image::make('images_anons/' . $image['src'])->width()

Is making this error: Intervention\Image\Exception\NotReadableException: Image source not readable Can you tell me why and how to solve this problem ? Besides on my page I'm getting what I want, image width so it's working but not in unit test.