code: def test_read_cell_explicit_start(
      pynb="""
  import pandas as pd
  # +
  def data():
      return pd.DataFrame({'A': [0, 1]})
  
  
  data()
  """,
  ):
      nb = jupytext.reads(pynb, "py")
      pynb2 = jupytext.writes(nb, "py")
      compare(pynb2, pynb)
  
imports: import pytest
  from nbformat.v4.nbbase import new_code_cell, new_markdown_cell, new_notebook, new_raw_cell
  import jupytext
  from jupytext.compare import compare, compare_notebooks
label_desc: Use image node_id 7 for calling a global function with example usage: test_read_cell_explicit_start(pynb) without return types