code: def test_compare_on_notebooks(notebook_actual, notebook_expected):
      with pytest.raises(AssertionError) as err:
          compare(notebook_actual, notebook_expected)
  
      assert (
          str(err.value)
          == """
  --- expected
  +++ actual
  @@ -18,7 +18,7 @@
      "cell_type": "markdown",
      "id": "markdown-cell-two",
      "metadata": {},
  -   "source": "Second markdown cell"
  +   "source": "Modified markdown cell"
     }
    ],
    "metadata": {
  @@ -37,7 +37,7 @@
      "name": "python",
      "nbconvert_exporter": "python",
      "pygments_lexer": "ipython3",
  -   "version": "3.7.3"
  +   "version": "3.6.8"
     },
     "toc": {
      "base_numbering": 1,"""
      )
  
imports: import pytest
  from nbformat.v4.nbbase import new_code_cell, new_markdown_cell, new_notebook, new_raw_cell
  from jupytext.compare import NotebookDifference, compare, compare_cells, compare_notebooks
  from jupytext.compare import test_round_trip_conversion
label_desc: Use image node_id 4 for calling a global function with example usage: test_compare_on_notebooks(notebook_actual, notebook_expected) without return types