def dist(a, b):
    return sum((i-j)**2 for i, j in zip(a, b))
def test_populate_old_value_of_change_with_invalid_state(self):
        self.save_new_default_exploration('exp1', self.author_id)
        expected_suggestion_dict = self.suggestion_dict
        suggestion = suggestion_registry.SuggestionEditStateContent(
            expected_suggestion_dict['suggestion_id'],
            expected_suggestion_dict['target_id'],
            expected_suggestion_dict['target_version_at_submission'],
            expected_suggestion_dict['status'], self.author_id,
            self.reviewer_id, expected_suggestion_dict['change'],
            expected_suggestion_dict['score_category'],
            expected_suggestion_dict['language_code'], False, self.fake_date)

        suggestion.change.state_name = 'invalid_state_name'

        self.assertIsNone(suggestion.change.old_value)

        suggestion.populate_old_value_of_change()

        self.assertIsNone(suggestion.change.old_value)