code: def test_header_to_metadata_and_cell_metadata():
      text = """---
  title: Sample header
  jupyter:
    mainlanguage: python
  ---
  """
      lines = text.splitlines()
      metadata, _, cell, pos = header_to_metadata_and_cell(
          lines, "", ""
      )
  
      assert metadata == {"mainlanguage": "python"}
      assert cell.cell_type == "raw"
      assert (
          cell.source
          == """---
  title: Sample header
  ---"""
      )
      assert cell.metadata == {"lines_to_next_cell": 0}
      assert pos == len(lines)
  
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 4 for calling a global function with example usage: test_header_to_metadata_and_cell_metadata() without return types