code: def duplicate_columns_frame():
      """Dataframe with duplicate column names."""
      return DataFrame(
          np.random.default_rng(2).standard_normal((1500, 4)),
          columns=["a", "a", "b", "b"],
      )
  
imports: from io import StringIO
  import re
  from string import ascii_uppercase
  import sys
  import textwrap
  import numpy
  import pytest
  from pandas.compat import IS64, PYPY
  from pandas import CategoricalIndex, DataFrame, MultiIndex, Series, date_range, option_context
  import pandas._testing
label_desc: Use image node_id 1 for calling a global function with example usage: duplicate_columns_frame() and returns: DataFrame