Test event callback exception handling

Author: tpoliaw

tests/unit_tests/core/test_event.py

@@ -2,6 +2,7 @@
 from concurrent.futures import Future
 from dataclasses import dataclass
 from queue import Queue
+from unittest import mock
 
 import pytest
 
@@ -76,6 +77,21 @@ def test_correlation_id(publisher: EventPublisher[MyEvent]) -> None:
     assert f.result(timeout=_TIMEOUT) == correlation_id
 
 
+def test_callback_exceptions_are_contained(publisher: EventPublisher[MyEvent]):
+    event = MyEvent("foo")
+    c_id = "bar"
+
+    # First call should raise exception, next should be fine
+    handler = mock.Mock(side_effect=[ValueError("Bad Event"), ()])
+    publisher.subscribe(handler)
+    publisher.subscribe(handler)
+
+    publisher.publish(event, c_id)
+
+    # Both handlers should be called and the exception should not be raised from publish
+    handler.assert_has_calls([mock.call(event, c_id), mock.call(event, c_id)])
+
+
 def _drain(queue: Queue) -> Iterable:
     while not queue.empty():
         yield queue.get_nowait()