code: def test_notebookdatabase_empty_output(tmp_directory):
      nb = """
  # + tags=["empty"]
  x = 1
  """
  
      save_notebook(nb, "nb.ipynb")
      db = NotebookDatabase("nb.db", "*.ipynb")
      db.index()
  
      out = db.query(
          """
  SELECT
      path,
      json_extract(c, '$.empty') AS plot
  FROM nbs
  """
      )
  
      assert out is not None
  
file_path: sklearn-evaluation/tests/nb/test_NotebookDatabase.py
imports: from pathlib import Path
  import pytest
  from sklearn_evaluation import NotebookDatabase
  from conftest import save_notebook
label_desc: Use image node_id 3 for calling a global function with example usage: test_notebookdatabase_empty_output(tmp_directory) without return types