use warnings.warn for DeciderFeatureNotFoundException in get_variant_without_expose()

Author: mrlevitas

reddit_decider/__init__.py

@@ -386,6 +386,9 @@ def get_variant_without_expose(self, experiment_name: str) -> Optional[str]:
 
         try:
             decision = self._rs_decider.choose(experiment_name, ctx)
+        except DeciderFeatureNotFoundException as exc:
+            warnings.warn(exc)
+            return None
         except DeciderException as exc:
             logger.info(exc)
             return None

tests/decider_tests.py

@@ -569,6 +569,27 @@ def test_get_variant_without_expose_for_holdout_exposure(self):
                 experiment_name="hg", variant="holdout", event_fields=event_fields
             )
 
+    def test_none_returned_on_get_variant_without_expose_call_with_experiment_not_found(self):
+        with create_temp_config_file({}) as f:
+            decider = setup_decider(f, self.minimal_decider_context, self.mock_span, self.event_logger)
+
+            self.assertEqual(self.event_logger.log.call_count, 0)
+            with warnings.catch_warnings(record=True) as captured:
+                variant = decider.get_variant_without_expose("anything")
+
+                # can't test warning log only shows up only once if `decider.get_variant("anything")`
+                # is called again due to bug in `catch_warnings` contextmanager
+                # see https://github.com/python/cpython/issues/73858
+                assert any(
+                    'Feature "anything" not found.'
+                    in str(x.message)
+                    for x in captured
+                )
+            self.assertEqual(variant, None)
+
+            # no exposures should be triggered
+            self.assertEqual(self.event_logger.log.call_count, 0)
+
     def test_get_variant_for_identifier_user_id(self):
         identifier = USER_ID
         bucket_val = "user_id"