code: def test_output_sheetnames_none():
      """Test output if sheetnames is None."""
      result = (
          io.xlsx_cells(wb, sheetnames=None, font=True)["pivot-notes"][
              "font"
          ]
          .str.get("name")
          .tolist()
      )
      assert "Calibri" in result
  
imports: from pathlib import Path
  import pytest
  from openpyxl import load_workbook
  from pandas.testing import assert_series_equal
  from janitor import io
label_desc: Use image node_id 18 for calling a global function with example usage: test_output_sheetnames_none() without return types