code: def df_constant_columns():
      """Return a dataframe that has columns with constant values."""
      data = {
          "a": [1] * 9,
          "Bell__Chart": [1.234_523_45, 2.456_234, 3.234_612_5] * 3,
          "decorated-elephant": [1, 2, 3] * 3,
          "animals@#$%^": ["rabbit"] * 9,
          "cities": ["Cambridge", "Shanghai", "Basel"] * 3,
      }
      df = pd.DataFrame(data)
      return df
  
file_path: pyjanitor/tests/conftest.py
imports: import os
  import numpy
  import pandas
  import pytest
  from janitor.testing_utils import date_data
label_desc: Use image node_id 12 for calling a global function with example usage: df_constant_columns() and returns: df