diff --git a/durabletask/testing/in_memory_backend.py b/durabletask/testing/in_memory_backend.py
index 590688ad..21417184 100644
--- a/durabletask/testing/in_memory_backend.py
+++ b/durabletask/testing/in_memory_backend.py
@@ -277,6 +277,10 @@ def predicate(inst: OrchestrationInstance) -> bool:
         instance = self._wait_for_state(request.instanceId, predicate, timeout=context.time_remaining())
 
         if not instance:
+            with self._lock:
+                if request.instanceId in self._instances:
+                    context.abort(grpc.StatusCode.DEADLINE_EXCEEDED,
+                                  f"Timed out waiting for instance '{request.instanceId}' to start")
             return pb.GetInstanceResponse(exists=False)
 
         return self._build_instance_response(instance, request.getInputsAndOutputs)
@@ -290,6 +294,10 @@ def WaitForInstanceCompletion(self, request: pb.GetInstanceRequest, context):
         )
 
         if not instance:
+            with self._lock:
+                if request.instanceId in self._instances:
+                    context.abort(grpc.StatusCode.DEADLINE_EXCEEDED,
+                                  f"Timed out waiting for instance '{request.instanceId}' to complete")
             return pb.GetInstanceResponse(exists=False)
 
         return self._build_instance_response(instance, request.getInputsAndOutputs)
@@ -309,7 +317,14 @@ def RaiseEvent(self, request: pb.RaiseEventRequest, context):
             )
             instance.pending_events.append(event)
             instance.last_updated_at = datetime.now(timezone.utc)
-            self._enqueue_orchestration(instance.instance_id)
+
+            # Don't dispatch work for suspended or terminal orchestrations;
+            # suspended events will be delivered when the orchestration is
+            # resumed, and terminal orchestrations can't process new events.
+            not_terminal = not self._is_terminal_status(instance.status)
+            not_suspended = instance.status != pb.ORCHESTRATION_STATUS_SUSPENDED
+            if not_terminal and not_suspended:
+                self._enqueue_orchestration(instance.instance_id)
 
         self._logger.info(f"Raised event '{request.name}' for instance '{request.instanceId}'")
         return pb.RaiseEventResponse()