code: def test_sort_index_na_position(self):
      series = Series(index=[3, 2, 1, 4, 3, np.nan], dtype=object)
      expected_series_first = Series(
          index=[np.nan, 1, 2, 3, 3, 4], dtype=object
      )
  
      index_sorted_series = series.sort_index(na_position="first")
      tm.assert_series_equal(expected_series_first, index_sorted_series)
  
      expected_series_last = Series(
          index=[1, 2, 3, 3, 4, np.nan], dtype=object
      )
  
      index_sorted_series = series.sort_index(na_position="last")
      tm.assert_series_equal(expected_series_last, index_sorted_series)
  
imports: import numpy
  import pytest
  from pandas import DatetimeIndex, IntervalIndex, MultiIndex, Series
  import pandas._testing
label_desc: Use image node_id 7 for calling the TestSeriesSortIndex obj's underlying member method code with example usage: obj.test_sort_index_na_position() without return types