ENH: Raise error if no events found when calling get_events

skipci

octue/cloud/pub_sub/bigquery.py

@@ -3,6 +3,7 @@
 from google.cloud.bigquery import Client, QueryJobConfig, ScalarQueryParameter
 
 from octue.cloud.events.validation import VALID_EVENT_KINDS
+from octue.exceptions import ServiceNotFound
 from octue.resources import Manifest
 
 
@@ -15,6 +16,8 @@ def get_events(table_id, sender, question_uuid, kind=None, include_backend_metad
     :param str|None kind: the kind of event to get; if `None`, all event kinds are returned
     :param bool include_backend_metadata: if `True`, include the service backend metadata
     :param int limit: the maximum number of events to return
+    :raise ValueError: if the `kind` parameter is invalid
+    :raise octue.exceptions.ServiceNotFound: if the sender hasn't emitted any events related to the question UUID (or any events at all)
     :return list(dict): the events for the question
     """
     if kind:
@@ -64,8 +67,15 @@ def get_events(table_id, sender, question_uuid, kind=None, include_backend_metad
     )
 
     query_job = client.query(query, job_config=job_config)
-    rows = query_job.result()
-    df = rows.to_dataframe()
+    result = query_job.result()
+
+    if result.total_rows == 0:
+        raise ServiceNotFound(
+            f"No events found. The requested sender {sender!r} may not exist or it hasn't emitted any events for "
+            f"question {question_uuid!r} (or any events at all)."
+        )
+
+    df = result.to_dataframe()
 
     # Convert JSON strings to python primitives.
     df["event"] = df["event"].map(json.loads)

tests/cloud/pub_sub/test_bigquery.py

@@ -1,7 +1,25 @@
 from unittest import TestCase
-from unittest.mock import patch
+from unittest.mock import MagicMock, patch
 
 from octue.cloud.pub_sub.bigquery import get_events
+from octue.exceptions import ServiceNotFound
+
+
+class MockEmptyResult:
+    """A mock empty query result."""
+
+    def __init__(self, total_rows=0):
+        self.total_rows = total_rows
+
+    def result(self):
+        return MagicMock(total_rows=self.total_rows)
+
+
+class MockEmptyBigQueryClient:
+    """A mock BigQuery client that returns a mock empty query result."""
+
+    def query(self, *args, **kwargs):
+        return MockEmptyResult()
 
 
 class TestGetEvents(TestCase):
@@ -15,6 +33,12 @@ def test_error_raised_if_event_kind_invalid(self):
                 kind="frisbee_tournament",
             )
 
+    def test_error_raised_if_no_events_found(self):
+        """Test that an error is raised if no events are found."""
+        with patch("octue.cloud.pub_sub.bigquery.Client", MockEmptyBigQueryClient):
+            with self.assertRaises(ServiceNotFound):
+                get_events(table_id="blah", sender="octue/test-service:1.0.0", question_uuid="blah")
+
     def test_without_kind(self):
         """Test the query used to retrieve events of all kinds."""
         with patch("octue.cloud.pub_sub.bigquery.Client") as mock_client: