def METHOD_NAME(self, img, frames, slides=5):
    # check whether it really changes the images
    # in the anim_delay interval
    old = None
    while slides:
        # different frames, sequence is changing
        self.assertNotEqual(img.anim_index, old)
        old = img.anim_index
        self.advance_frames(frames)
        slides -= 1
    return True