'thumbnail_if_set() returns self.thumbnail if set, or else returns
self.file'

def test_thumbnail_if_set(self):

    image = ImageAttachment(content_object=self.obj, creator=self.user)
    with open('kitsune/upload/tests/media/test.jpg') as f:
        up_file = File(f)
        image.file.save(up_file.name, up_file, save=True)
    eq_(image.file, image.thumbnail_if_set())
    generate_thumbnail(image, 'file', 'thumbnail')
    eq_(image.thumbnail, image.thumbnail_if_set())
