code: def test_jupytext_can_read_nbformat_3(
      sample_notebook_v3_json,
  ):
      with pytest.warns(
          Warning, match="jupyter nbconvert --to notebook --inplace"
      ):
          nb = reads(sample_notebook_v3_json, fmt="ipynb")
          assert nb["nbformat"] == 3
  
      nb = reads(sample_notebook_v3_json, as_version=4, fmt="ipynb")
      assert nb["nbformat"] == 4
  
file_path: jupytext/tests/functional/others/test_nbformat_version.py
imports: import pytest
  from nbformat import writes
  from nbformat.v3.nbbase import new_code_cell, new_notebook, new_text_cell, new_worksheet
  from nbformat.v4.nbbase import new_markdown_cell
  from nbformat.v4.nbbase import new_notebook
  from jupytext import reads, writes
  from jupytext.jupytext import NotSupportedNBFormatVersion
label_desc: Use image node_id 4 for calling a global function with example usage: test_jupytext_can_read_nbformat_3(sample_notebook_v3_json) without return types