code: def test_header_to_html_comment(no_jupytext_version_number):
      metadata = {"jupytext": {"mainlanguage": "python"}}
      nb = new_notebook(metadata=metadata, cells=[])
      header, lines_to_next_cell = metadata_and_cell_to_header(
          nb,
          metadata,
          get_format_implementation(".md"),
          {"extension": ".md", "hide_notebook_metadata": True},
      )
      compare(
          "\n".join(header),
          """<!--
  
  ---
  jupyter:
    jupytext:
      mainlanguage: python
  ---
  
  -->""",
      )
  
file_path: jupytext/tests/unit/test_header.py
imports: from nbformat.v4.nbbase import new_markdown_cell, new_notebook, new_raw_cell
  import jupytext
  from jupytext.compare import compare
  from jupytext.formats import get_format_implementation
  from jupytext.header import header_to_metadata_and_cell, metadata_and_cell_to_header, uncomment_line
label_desc: Use image node_id 10 for calling a global function with example usage: test_header_to_html_comment(no_jupytext_version_number) without return types