code: def contains(ref_value):
      
      def contains_ref_value(x):
          if ref_value in x:
              return True
          else:
              raise DoesNotContainValue(wrong_value=x, ref_value=ref_value)
  
      contains_ref_value.__name__ = 'contains_{}'.format(ref_value)
      return contains_ref_value
docs: 'Contains' validation_function generator.
      Returns a validation_function to check that `ref_value in x`
  
      :param ref_value: a value that must be present in x
      :return: