code: def test_ascending_sort(self):
      result = msno.nullity_sort(self.df, sort="ascending")
      expected = self.df.iloc[[2, 1, 0]]
      assert result.equals(expected)
  
imports: import unittest
  import pandas
  import numpy
  import sys
  import missingno
label_desc: Use image node_id 3 for calling the TestNullitySort obj's underlying member method code with example usage: obj.test_ascending_sort() without return types