def test_blocksize(self): s = BytesIO(b"1234567890abcdefghijklmnopqrstuvwxyz") s = tcp.Reader(s) s.BLOCKSIZE = 2 assert s.read(1) == b"1" assert s.read(2) == b"23" assert s.read(3) == b"456" assert s.read(4) == b"7890" d = s.read(-1) assert d.startswith(b"abc") and d.endswith(b"xyz")