… done so far and provide feedback for Jules to continue.

This commit introduces a comprehensive test suite for the Python scripts
located in the examples/account_management directory.

Key changes include:

1.  Created a new `tests` subdirectory within
    `examples/account_management`.
2.  Added `__init__.py` files to ensure proper module discovery.
3.  Wrote unit tests for each of the 9 scripts in
    `examples/account_management`:
    - `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`
    - `update_user_access.py`
    - `verify_advertiser_identity.py`
    These tests utilize mocking extensively to simulate API interactions
    with the Google Ads API (v19) and verify the logic of each script,
    including argument parsing, service calls, and output formatting.
4.  Added a test runner script, `tests/run_tests.py`, which uses the
    `unittest` module to discover and execute all tests in the suite.
    The runner script ensures that the example scripts can be imported
    correctly by adjusting `sys.path`.
5.  Created a `tests/README.md` file providing instructions on how to
    run the tests and outlining any prerequisites.

All tests pass, ensuring the reliability and correctness of the
account management example scripts.

The test `test_main_prints_change_details` in
`examples/account_management/tests/test_get_change_details.py` was
failing with `unittest.mock.InvalidSpecError: Cannot spec a Mock object`.

This error occurred because `MagicMock` instances for
`event.old_resource` and `event.new_resource` were being created
by passing the already existing `MagicMock` (which `event.old_resource`
was by virtue of `event` being a `MagicMock`) as the `spec` argument.
A mock instance cannot be used as a spec for another mock.

The fix involves removing the `spec` argument from the initialization
of `event.old_resource` and `event.new_resource` mock objects.
These are now initialized as `MagicMock()` without a spec, which is
appropriate for their usage in the test, where their attributes are
subsequently defined.

The individual test `test_get_change_details.py` now passes, and the
full test suite in `examples/account_management/tests` also passes,
confirming the fix and no regressions.