code: def test_not_installed():
      with mock.patch(
          "jupytext.formats.JUPYTEXT_FORMATS", return_value=[]
      ):
          with pytest.raises(JupytextFormatError):
              get_format_implementation(".myst")
  
imports: import json
  import unittest.mock
  from textwrap import dedent
  import pytest
  from nbformat.v4.nbbase import new_notebook
  from tornado.web import HTTPError
  import jupytext
  from jupytext.cli import jupytext
  from jupytext.compare import compare
  from jupytext.formats import JupytextFormatError, get_format_implementation, guess_format
  from jupytext.myst import CODE_DIRECTIVE, MystMetadataParsingError, matches_mystnb, myst_extensions, myst_to_notebook
label_desc: Use image node_id 6 for calling a global function with example usage: test_not_installed() without return types