Migrate Google example bigquery_to_mssql to new design AIP-47 (#25174)

related: #22447, #22430

Author: chenglongyan

airflow/providers/google/cloud/example_dags/example_bigquery_to_mssql.py renamed to tests/system/providers/google/cloud/bigquery/example_bigquery_to_mssql.py

@@ -30,18 +30,21 @@
 )
 from airflow.providers.google.cloud.transfers.bigquery_to_mssql import BigQueryToMsSqlOperator
 
+ENV_ID = os.environ.get("SYSTEM_TESTS_ENV_ID")
 PROJECT_ID = os.environ.get("GCP_PROJECT_ID", "example-project")
-DATASET_NAME = os.environ.get("GCP_BIGQUERY_DATASET_NAME", "test_dataset_transfer")
+DAG_ID = "example_bigquery_to_mssql"
+
+DATASET_NAME = f"dataset_{DAG_ID}_{ENV_ID}"
 DATA_EXPORT_BUCKET_NAME = os.environ.get("GCP_BIGQUERY_EXPORT_BUCKET_NAME", "INVALID BUCKET NAME")
 TABLE = "table_42"
 destination_table = "mssql_table_test"
 
 with models.DAG(
-    "example_bigquery_to_mssql",
-    schedule_interval=None,  # Override to match your needs
+    DAG_ID,
+    schedule_interval="@once",  # Override to match your needs
     start_date=datetime(2021, 1, 1),
     catchup=False,
-    tags=["example"],
+    tags=["example", "bigquery"],
 ) as dag:
     bigquery_to_mssql = BigQueryToMsSqlOperator(
         task_id="bigquery_to_mssql",
@@ -61,10 +64,28 @@
             {"name": "salary", "type": "INTEGER", "mode": "NULLABLE"},
         ],
     )
-    create_dataset >> create_table >> bigquery_to_mssql
 
     delete_dataset = BigQueryDeleteDatasetOperator(
         task_id="delete_dataset", dataset_id=DATASET_NAME, delete_contents=True
     )
 
-    bigquery_to_mssql >> delete_dataset
+    (
+        # TEST SETUP
+        create_dataset
+        >> create_table
+        # TEST BODY
+        >> bigquery_to_mssql
+        # TEST TEARDOWN
+        >> delete_dataset
+    )
+
+    from tests.system.utils.watcher import watcher
+
+    # This test needs watcher in order to properly mark success/failure
+    # when "tearDown" task with trigger rule is part of the DAG
+    list(dag.tasks) >> watcher()
+
+from tests.system.utils import get_test_run  # noqa: E402
+
+# Needed to run the example DAG with pytest (see: tests/system/README.md#run_via_pytest)
+test_run = get_test_run(dag)