def METHOD_NAME(self):
    # NOTE invariant based on GzipFile implementation
    zipper = mod.GzipStream(BytesIO(b""))
    zipper.read(10)
    assert zipper._buf.size == 0, f"invariant failed ({zipper._buf.size})"
    with self.assertRaises(GzipStreamError):
        zipper.content_length
    zipper.read()
    self.assertEqual(zipper.content_length, 0)