feat: Add initial tests for account_management examples

This commit introduces a test structure and initial tests for several
examples within the examples/account_management directory. All tests
are written to use Google Ads API v19 and leverage unittest.mock
for mocking API interactions.

The following examples now have test coverage:
- create_customer.py
- get_account_hierarchy.py
- get_change_details.py
- get_change_summary.py
- invite_user_with_access_role.py
- link_manager_to_client.py
- list_accessible_customers.py

Each test suite typically covers:
- Successful execution path and output verification.
- GoogleAdsException handling.
- Mocking of relevant Google Ads API services and client.

Further tests for remaining files in this directory will be added in
subsequent commits.

Author: google-labs-jules[bot]

tests/examples/__init__.py

@@ -0,0 +1,125 @@
+import unittest
+from unittest.mock import patch, MagicMock
+
+from google.ads.googleads.errors import GoogleAdsException
+# This import assumes that the test runner will add the root directory to sys.path
+# or that the `examples` directory is otherwise findable.
+from examples.account_management.create_customer import main
+
+
+class CreateCustomerTest(unittest.TestCase):
+
+    @patch("examples.account_management.create_customer.GoogleAdsClient.load_from_storage")
+    def test_create_customer_success(self, mock_load_from_storage):
+        """Tests the successful creation of a customer."""
+        # Create a mock GoogleAdsClient
+        mock_google_ads_client = MagicMock()
+        mock_load_from_storage.return_value = mock_google_ads_client
+
+        # Create a mock CustomerService
+        mock_customer_service = MagicMock()
+        mock_google_ads_client.get_service.return_value = mock_customer_service
+
+        # Mock the create_customer_client method to return a mock response object
+        # This response object structure might need adjustment based on what the actual method returns
+        # and what the main function does with it. For now, a simple MagicMock.
+        mock_create_customer_response = MagicMock()
+        mock_create_customer_response.resource_name = "customers/1234567890/customerClients/9876543210"
+        mock_customer_service.create_customer_client.return_value = mock_create_customer_response
+
+        # Define test arguments
+        manager_customer_id = "1234567890"
+        currency_code = "USD"
+        time_zone = "America/New_York"
+        # The descriptive_name is optional in the script, so we'll test with it.
+        descriptive_name = "Test Customer"
+
+        # Call the main function with test arguments
+        # The original script takes client_customer_id as an argument, but it's not used.
+        # The create_customer.py script expects:
+        # main(client, manager_customer_id, currency_code, time_zone, descriptive_name=None)
+        # We are mocking the client, so we pass the mock_google_ads_client
+        main(
+            mock_google_ads_client,
+            manager_customer_id,
+            currency_code,
+            time_zone,
+            descriptive_name,
+        )
+
+        # Assert that get_service was called with the correct service name and version
+        mock_google_ads_client.get_service.assert_called_once_with(
+            "CustomerService", version="v19"
+        )
+
+        # Assert that create_customer_client was called once with the correct parameters
+        # The original script builds a CustomerClient object. We need to check the attributes
+        # of the customer_client argument passed to create_customer_client.
+        self.assertEqual(mock_customer_service.create_customer_client.call_count, 1)
+        call_args = mock_customer_service.create_customer_client.call_args
+        
+        # call_args is a tuple (args, kwargs). We expect (customer_id, customer_client, modify)
+        # or (request=...) if using a request object.
+        # The script uses: customer_service.create_customer_client(customer_id=manager_customer_id, customer_client=customer_client)
+        self.assertEqual(call_args[1]['customer_id'], manager_customer_id)
+        
+        # Check the customer_client object passed
+        customer_client_arg = call_args[1]['customer_client']
+        self.assertEqual(customer_client_arg.descriptive_name, descriptive_name)
+        self.assertEqual(customer_client_arg.currency_code, currency_code)
+        self.assertEqual(customer_client_arg.time_zone, time_zone)
+        # The original script also sets client_customer.applied_labels, but only if an optional
+        # "labels" argument is provided to main(). We are not testing that here.
+
+
+    @patch("examples.account_management.create_customer.GoogleAdsClient.load_from_storage")
+    def test_create_customer_google_ads_exception(self, mock_load_from_storage):
+        """Tests handling of GoogleAdsException during customer creation."""
+        mock_google_ads_client = MagicMock()
+        mock_load_from_storage.return_value = mock_google_ads_client
+
+        mock_customer_service = MagicMock()
+        mock_google_ads_client.get_service.return_value = mock_customer_service
+
+        # Configure create_customer_client to raise GoogleAdsException
+        # The exception needs to be instantiated with a failure object.
+        # We can mock the failure object and its errors.
+        mock_failure = MagicMock()
+        mock_error = MagicMock()
+        mock_error.message = "Test GoogleAdsException"
+        mock_failure.errors = [mock_error]
+        google_ads_exception = GoogleAdsException(
+            mock_failure, "call", "trigger", "request_id", "error_code_enum"
+        )
+        mock_customer_service.create_customer_client.side_effect = google_ads_exception
+
+        manager_customer_id = "1234567890"
+        currency_code = "USD"
+        time_zone = "America/New_York"
+        descriptive_name = "Test Customer Exception"
+        
+        # We expect the main function to catch the GoogleAdsException and print an error message.
+        # To verify this, we can check if sys.exit(1) is called, or if specific error logging occurs.
+        # For simplicity, we'll assert that the exception is indeed raised and propagated
+        # to the test if not caught, or if caught, that the program exits or logs.
+        # The script's main function has a try-except block that prints the error and calls sys.exit(1).
+        # We can mock sys.exit to check if it's called.
+        with patch("sys.exit") as mock_sys_exit:
+            main(
+                mock_google_ads_client,
+                manager_customer_id,
+                currency_code,
+                time_zone,
+                descriptive_name,
+            )
+            # Assert that sys.exit was called, implying the exception was caught.
+            mock_sys_exit.assert_called_once_with(1)
+
+        mock_google_ads_client.get_service.assert_called_once_with(
+            "CustomerService", version="v19"
+        )
+        mock_customer_service.create_customer_client.assert_called_once()
+
+
+if __name__ == "__main__":
+    unittest.main()