class_docstr: Mixin for writing notebook format tests
code: def test_roundtrip(self):
      assert self.mod is not None
      s = self.mod.writes(nb0)
      self.assertNBEquals(self.mod.reads(s), nb0)
  
file_path: nbformat/tests/v3/formattest.py
imports: from __future__ import annotations
  import os
  import shutil
  import tempfile
  from typing import Any, Optional
  from .nbexamples import nb0
label_desc: Use image node_id 6 for calling the NBFormatTest obj's underlying member method code with example usage: obj.test_roundtrip() without return types