code: def test_sort_index_nan(self):
      # GH#3917
  
      # Test DataFrame with nan label
      df = DataFrame(
          {
              "A": [1, 2, np.nan, 1, 6, 8, 4],
              "B": [9, np.nan, 5, 2, 5, 4, 5],
          },
          index=[1, 2, 3, 4, 5, 6, np.nan],
      )
  
      # NaN label, ascending=True, na_position='last'
      sorted_df = df.sort_index(
          kind="quicksort", ascending=True, na_position="last"
      )
      expected = DataFrame(
          {
              "A": [1, 2, np.nan, 1, 6, 8, 4],
              "B": [9, np.nan, 5, 2, 5, 4, 5],
          },
          index=[1, 2, 3, 4, 5, 6, np.nan],
      )
      tm.assert_frame_equal(sorted_df, expected)
  
      # NaN label, ascending=True, na_position='first'
      sorted_df = df.sort_index(na_position="first")
      expected = DataFrame(
          {
              "A": [4, 1, 2, np.nan, 1, 6, 8],
              "B": [5, 9, np.nan, 5, 2, 5, 4],
          },
          index=[np.nan, 1, 2, 3, 4, 5, 6],
      )
      tm.assert_frame_equal(sorted_df, expected)
  
      # NaN label, ascending=False, na_position='last'
      sorted_df = df.sort_index(kind="quicksort", ascending=False)
      expected = DataFrame(
          {
              "A": [8, 6, 1, np.nan, 2, 1, 4],
              "B": [4, 5, 2, 5, np.nan, 9, 5],
          },
          index=[6, 5, 4, 3, 2, 1, np.nan],
      )
      tm.assert_frame_equal(sorted_df, expected)
  
      # NaN label, ascending=False, na_position='first'
      sorted_df = df.sort_index(
          kind="quicksort", ascending=False, na_position="first"
      )
      expected = DataFrame(
          {
              "A": [4, 8, 6, 1, np.nan, 2, 1],
              "B": [5, 4, 5, 2, 5, np.nan, 9],
          },
          index=[np.nan, 6, 5, 4, 3, 2, 1],
      )
      tm.assert_frame_equal(sorted_df, expected)
  
imports: import numpy
  import pytest
  import pandas
  from pandas import CategoricalDtype, CategoricalIndex, DataFrame, IntervalIndex, MultiIndex, RangeIndex, Series, Timestamp
  import pandas._testing
label_desc: Use image node_id 5 for calling the TestDataFrameSortIndex obj's underlying member method code with example usage: obj.test_sort_index_nan() without return types