code: def test_notebook_metadata_none():
      nb = new_notebook(
          metadata={"jupytext": {"notebook_metadata_filter": "-all"}}
      )
      text = writes(nb, "md")
      assert "---" not in text
  
imports: from copy import deepcopy
  import pytest
  from nbformat.v4.nbbase import new_code_cell, new_notebook
  from jupytext import reads, writes
  from jupytext.cli import jupytext
  from jupytext.compare import compare, compare_notebooks
  from jupytext.metadata_filter import filter_metadata, metadata_filter_as_dict
label_desc: Use image node_id 10 for calling a global function with example usage: test_notebook_metadata_none() without return types