code: def df_dup_cols(self):
      dups = ["A", "A", "C", "D"]
      df = DataFrame(
          np.arange(12).reshape(3, 4), columns=dups, dtype="float64"
      )
      return df
  
imports: import re
  import numpy
  import pytest
  from pandas import Categorical, CategoricalDtype, CategoricalIndex, DataFrame, DateOffset, DatetimeIndex, Index, MultiIndex, Series, Timestamp, concat, date_range, get_dummies, period_range
  import pandas._testing
  from pandas.core.arrays import SparseArray
label_desc: Use image node_id 3 for calling the TestGetitemBooleanMask obj's underlying member method code with example usage: obj.df_dup_cols() and returns: df