code: def test_apply_black_on_markdown_notebook(tmpdir):
      text = """---
  jupyter:
    kernelspec:
      display_name: Python 3
      language: python
      name: python3
    language_info:
      codemirror_mode:
        name: ipython
        version: 3
      file_extension: .py
      mimetype: text/x-python
      name: python
      nbconvert_exporter: python
      pygments_lexer: ipython3
      version: 3.7.4
  ---
  
  ```python
  1    +     \
  2+3\
  +4
  ```
  """
      tmp_md = str(tmpdir.join("test.md"))
      with open(tmp_md, "w") as fp:
          fp.write(text)
  
      jupytext([tmp_md, "--pipe", "black"])
  
      nb = read(tmp_md)
      compare_cells(
          nb.cells, [new_code_cell("1 + 2 + 3 + 4")], compare_ids=False
      )
  
imports: import os
  from copy import deepcopy
  from shutil import copyfile
  import pytest
  from nbformat.v4.nbbase import new_code_cell, new_notebook
  from jupytext import read, write
  from jupytext.cli import jupytext, pipe_notebook, system
  from jupytext.combine import black_invariant
  from jupytext.compare import compare, compare_cells, compare_notebooks
  from jupytext.header import _DEFAULT_NOTEBOOK_METADATA
label_desc: Use image node_id 8 for calling a global function with example usage: test_apply_black_on_markdown_notebook(tmpdir) without return types