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Resolve test event ordering flakiness (#1194)

618cee5223bd9299d26486cb5e36e5d9d3ae4c88 · 2026-01-18 20:33:20 +0000 · rltakashige

## Motivation

mp sender occasionally does not have time to flush its events before
collect() is called, making the event ordering test fail.

## Changes

- Replace mp_channel with simple collector for event ordering test
- Also suppress warning for <frozen importlib._bootstrap>:488 <frozen
importlib._bootstrap>:488: DeprecationWarning: builtin type SwigPyObject
has no __module__ attribute


## Why It Works

<!-- Explain why your approach solves the problem -->

## Test Plan

### Manual Testing
<!-- Hardware: (e.g., MacBook Pro M1 Max 32GB, Mac Mini M2 16GB,
connected via Thunderbolt 4) -->
<!-- What you did: -->
<!-- - -->

### Automated Testing
Ran the test 100 times without it failing.

Files touched

Diff

commit 618cee5223bd9299d26486cb5e36e5d9d3ae4c88
Author: rltakashige <rl.takashige@gmail.com>
Date:   Sun Jan 18 20:33:20 2026 +0000

    Resolve test event ordering flakiness (#1194)
    
    ## Motivation
    
    mp sender occasionally does not have time to flush its events before
    collect() is called, making the event ordering test fail.
    
    ## Changes
    
    - Replace mp_channel with simple collector for event ordering test
    - Also suppress warning for <frozen importlib._bootstrap>:488 <frozen
    importlib._bootstrap>:488: DeprecationWarning: builtin type SwigPyObject
    has no __module__ attribute
    
    
    ## Why It Works
    
    <!-- Explain why your approach solves the problem -->
    
    ## Test Plan
    
    ### Manual Testing
    <!-- Hardware: (e.g., MacBook Pro M1 Max 32GB, Mac Mini M2 16GB,
    connected via Thunderbolt 4) -->
    <!-- What you did: -->
    <!-- - -->
    
    ### Automated Testing
    Ran the test 100 times without it failing.
---
 pyproject.toml                                     |  3 +++
 .../unittests/test_runner/test_event_ordering.py   | 25 ++++++++++++++++------
 2 files changed, 22 insertions(+), 6 deletions(-)

diff --git a/pyproject.toml b/pyproject.toml
index 9cdc3220..5f4fa7ea 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -126,3 +126,6 @@ env = [
   "EXO_TESTS=1"
 ]
 addopts = "-m 'not slow'"
+filterwarnings = [
+    "ignore:builtin type Swig:DeprecationWarning",
+]
diff --git a/src/exo/worker/tests/unittests/test_runner/test_event_ordering.py b/src/exo/worker/tests/unittests/test_runner/test_event_ordering.py
index e1744d1b..a8b4b1a5 100644
--- a/src/exo/worker/tests/unittests/test_runner/test_event_ordering.py
+++ b/src/exo/worker/tests/unittests/test_runner/test_event_ordering.py
@@ -121,6 +121,21 @@ def patch_out_mlx(monkeypatch: pytest.MonkeyPatch):
     monkeypatch.setattr(mlx_runner, "mlx_generate", fake_generate)
 
 
+# Use a fake event_sender to remove test flakiness.
+class EventCollector:
+    def __init__(self) -> None:
+        self.events: list[Event] = []
+
+    def send(self, event: Event) -> None:
+        self.events.append(event)
+
+    def close(self) -> None:
+        pass
+
+    def join(self) -> None:
+        pass
+
+
 def _run(tasks: Iterable[Task]):
     bound_instance = get_bound_mlx_ring_instance(
         instance_id=INSTANCE_1_ID,
@@ -130,22 +145,20 @@ def _run(tasks: Iterable[Task]):
     )
 
     task_sender, task_receiver = mp_channel[Task]()
-    event_sender, event_receiver = mp_channel[Event]()
+    event_sender = EventCollector()
 
-    with task_sender, event_receiver:
+    with task_sender:
         for t in tasks:
             task_sender.send(t)
 
         # worst monkeypatch known to man
         # this is some c++ nonsense
-        event_sender.close = nothin
-        event_sender.join = nothin
         task_receiver.close = nothin
         task_receiver.join = nothin
 
-        mlx_runner.main(bound_instance, event_sender, task_receiver)
+        mlx_runner.main(bound_instance, event_sender, task_receiver)  # type: ignore[arg-type]
 
-        return event_receiver.collect()
+        return event_sender.events
 
 
 def test_events_processed_in_correct_order(patch_out_mlx: pytest.MonkeyPatch):

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