How to use the sigal.image.generate_thumbnail function in sigal

def test_generate_thumbnail(tmpdir, image, path, wide_size, high_size):
    "Test the generate_thumbnail function."

    dstfile = str(tmpdir.join(image))
    for size in [(200, 150), (150, 200)]:
        generate_thumbnail(path, dstfile, size)
        im = Image.open(dstfile)
        assert im.size == size

    for size, thumb_size in [((200, 150), wide_size),
                             ((150, 200), high_size)]:
        generate_thumbnail(path, dstfile, size, fit=False)
        im = Image.open(dstfile)
        assert im.size == thumb_size

def test_generate_thumbnail(tmpdir, image, path, wide_size, high_size):
    "Test the generate_thumbnail function."

    dstfile = str(tmpdir.join(image))
    for size in [(200, 150), (150, 200)]:
        generate_thumbnail(path, dstfile, size)
        im = Image.open(dstfile)
        assert im.size == size

    for size, thumb_size in [((200, 150), wide_size),
                             ((150, 200), high_size)]:
        generate_thumbnail(path, dstfile, size, fit=False)
        im = Image.open(dstfile)
        assert im.size == thumb_size

def thumbnail(self):
        """Path to the thumbnail image (relative to the album directory)."""

        if not isfile(self.thumb_path):
            self.logger.debug('Generating thumbnail for %r', self)
            path = (self.dst_path if os.path.exists(self.dst_path)
                    else self.src_path)
            try:
                # if thumbnail is missing (if settings['make_thumbs'] is False)
                s = self.settings
                if self.type == 'image':
                    image.generate_thumbnail(
                        path, self.thumb_path, s['thumb_size'],
                        fit=s['thumb_fit'])
                elif self.type == 'video':
                    video.generate_thumbnail(
                        path, self.thumb_path, s['thumb_size'],
                        s['thumb_video_delay'], fit=s['thumb_fit'],
                        converter=s['video_converter'])
            except Exception as e:
                self.logger.error('Failed to generate thumbnail: %s', e)
                return
        return url_from_path(self.thumb_name)

def generate_thumbnail(source, outname, box, delay, fit=True, options=None,
                       converter='ffmpeg'):
    """Create a thumbnail image for the video source, based on ffmpeg."""

    logger = logging.getLogger(__name__)
    tmpfile = outname + ".tmp.jpg"

    # dump an image of the video
    cmd = [converter, '-i', source, '-an', '-r', '1',
           '-ss', delay, '-vframes', '1', '-y', tmpfile]
    logger.debug('Create thumbnail for video: %s', ' '.join(cmd))
    check_subprocess(cmd, source, outname)

    # use the generate_thumbnail function from sigal.image
    image.generate_thumbnail(tmpfile, outname, box, fit=fit, options=options)
    # remove the image
    os.unlink(tmpfile)