old_contents: import unittest
  
  from HARK.validators import non_empty
  
  class ValidatorsTests(unittest.TestCase):
      '''
      Tests for validator decorators which validate function arguments
      '''
  
      def test_non_empty(self):
          @non_empty('list_a')
          def foo(list_a, list_b):
              pass
  
          try:
              foo([1], [])
          except Exception:
              self.fail()
              
          if sys.version[0] == 2:
              with self.assertRaisesRegexp(
                  TypeError,
                  'Expected non-empty argument for parameter list_a',
              ):
                  foo([], [1])
          else:            
              with self.assertRaisesRegex(
                  TypeError,
                  'Expected non-empty argument for parameter list_a',
              ):
                  foo([], [1])
  
          @non_empty('list_a', 'list_b')
          def foo(list_a, list_b):
              pass
  
          with self.assertRaisesRegex(
              TypeError,
              'Expected non-empty argument for parameter list_b',
          ):
              foo([1], [])
          with self.assertRaisesRegex(
              TypeError,
              'Expected non-empty argument for parameter list_a',
          ):
              foo([], [1])
  
new_contents: import unittest, sys
  
  from HARK.validators import non_empty
  
  class ValidatorsTests(unittest.TestCase):
      '''
      Tests for validator decorators which validate function arguments
      '''
  
      def test_non_empty(self):
          @non_empty('list_a')
          def foo(list_a, list_b):
              pass
  
          try:
              foo([1], [])
          except Exception:
              self.fail()
              
          if sys.version[0] == 2:
              with self.assertRaisesRegexp(
                  TypeError,
                  'Expected non-empty argument for parameter list_a',
              ):
                  foo([], [1])
          else:            
              with self.assertRaisesRegex(
                  TypeError,
                  'Expected non-empty argument for parameter list_a',
              ):
                  foo([], [1])
  
          @non_empty('list_a', 'list_b')
          def foo(list_a, list_b):
              pass
  
          with self.assertRaisesRegex(
              TypeError,
              'Expected non-empty argument for parameter list_b',
          ):
              foo([1], [])
          with self.assertRaisesRegex(
              TypeError,
              'Expected non-empty argument for parameter list_a',
          ):
              foo([], [1])
  
subject: Fix import error