code: def test_roundtrip(self):
      s = writes(nb0)
      self.assertEqual(reads(s), nb0)
  
imports: from __future__ import annotations
  from unittest import TestCase
  from nbformat.v1.nbjson import reads, writes
  from .nbexamples import nb0
label_desc: Use image node_id 1 for calling the TestJSON obj's underlying member method code with example usage: obj.test_roundtrip() without return types