feat: Add test suite for examples/reporting

Adds a comprehensive test suite for the `parallel_report_download.py` script located in the `examples/reporting/` directory.

The test suite is created in `examples/reporting/tests/` and includes:
- Unit tests for individual functions: `generate_inputs`, `issue_search_request` (including success, API error handling, and retry logic).
- Integration tests for the `main()` function and the script's `if __name__ == "__main__":` entry point, covering argument parsing and client initialization.
- Mocking of external dependencies, particularly the GoogleAdsClient and its services, to allow tests to run without live API calls.
- Verification that the Google Ads API v19 is utilized, aligning with the script's existing configuration.

The `campaign_query` and `ad_group_query` in `parallel_report_download.py` were moved to module-level constants to facilitate easier testing.

Author: google-labs-jules[bot]

examples/reporting/parallel_report_download.py

@@ -35,6 +35,16 @@
 # Maximum number of retries for errors.
 MAX_RETRIES = 5
 
+# Define the GAQL query strings to run for each customer ID.
+campaign_query = """
+        SELECT campaign.id, metrics.impressions, metrics.clicks
+        FROM campaign
+        WHERE segments.date DURING LAST_30_DAYS"""
+ad_group_query = """
+        SELECT campaign.id, ad_group.id, metrics.impressions, metrics.clicks
+        FROM ad_group
+        WHERE segments.date DURING LAST_30_DAYS"""
+
 
 def main(
     client: GoogleAdsClient, customer_ids: List[str]
@@ -46,16 +56,6 @@ def main(
         customer_ids: an array of client customer IDs.
     """
 
-    # Define the GAQL query strings to run for each customer ID.
-    campaign_query = """
-        SELECT campaign.id, metrics.impressions, metrics.clicks
-        FROM campaign
-        WHERE segments.date DURING LAST_30_DAYS"""
-    ad_group_query = """
-        SELECT campaign.id, ad_group.id, metrics.impressions, metrics.clicks
-        FROM ad_group
-        WHERE segments.date DURING LAST_30_DAYS"""
-
     inputs: Iterable[Tuple[GoogleAdsClient, str, str]] = generate_inputs(
         client, customer_ids, [campaign_query, ad_group_query]
     )