def test_add_new_string_field_with_update_documents_api(self):
        """Test that adding new string fields via update_documents fails.
        
        This test verifies that attempting to add new string fields during an update operation
        results in appropriate error responses, as these field types cannot be added after 
        initial document creation.
        """
        # First add a minimal document with just an ID and a tensor field
        initial_doc = [{
            '_id': 'string_field_update_doc',
            'tensor_field': 'initial content'  # Need at least one field for indexing
        }]
        
        # Add the minimal document
        add_docs_response = self.client.index(self.text_index_name).add_documents(
            documents=initial_doc,
            tensor_fields=['tensor_field']
        )
        self.assertFalse(add_docs_response["errors"])
        
        # Try to update with a new string field
        update_docs_response = self.client.index(self.text_index_name).update_documents([{
            '_id': 'string_field_update_doc',
            'new_string_field': 'This should also fail'
        }])
        
        # Verify that errors were returned
        self.assertTrue(update_docs_response["errors"], 
                       "Expected error when adding new string field but got success")
        
        # Check the error details
        error_details = update_docs_response["items"][0]
        self.assertEqual(error_details["status"], 400, 
                        "Expected status code 400 for string field but got {error_details['status']}")

        # Assert the error message
        self.assertIn("new_string_field of type str does not exist in the original document. "
                      "Marqo does not support adding new lexical fields in partial updates"
                      , error_details["error"])
Test that adding new string fields via update_documents fails.
        
        This test verifies that attempting to add new string fields during an update operation
        results in appropriate error responses, as these field types cannot be added after 
        initial document creation.
        
tests/api_tests/v1/tests/api_tests/unstructured_index/test_update_documents_unstructured_index.py