code: def test_drop_multiindex_not_lexsorted(self):
      # GH#11640
  
      # define the lexsorted version
      lexsorted_mi = MultiIndex.from_tuples(
          [("a", ""), ("b1", "c1"), ("b2", "c2")], names=["b", "c"]
      )
      lexsorted_df = DataFrame([[1, 3, 4]], columns=lexsorted_mi)
      assert lexsorted_df.columns._is_lexsorted()
  
      # define the non-lexsorted version
      not_lexsorted_df = DataFrame(
          columns=["a", "b", "c", "d"],
          data=[[1, "b1", "c1", 3], [1, "b2", "c2", 4]],
      )
      not_lexsorted_df = not_lexsorted_df.pivot_table(
          index="a", columns=["b", "c"], values="d"
      )
      not_lexsorted_df = not_lexsorted_df.reset_index()
      assert not not_lexsorted_df.columns._is_lexsorted()
  
      expected = lexsorted_df.drop("a", axis=1).astype(float)
      with tm.assert_produces_warning(PerformanceWarning):
          result = not_lexsorted_df.drop("a", axis=1)
  
      tm.assert_frame_equal(result, expected)
  
imports: import re
  import numpy
  import pytest
  from pandas.errors import PerformanceWarning
  import pandas
  from pandas import DataFrame, DatetimeIndex, Index, MultiIndex, Series, Timestamp
  import pandas._testing
label_desc: Use image node_id 3 for calling the TestDataFrameDrop obj's underlying member method code with example usage: obj.test_drop_multiindex_not_lexsorted() without return types