From bf7bafff896f2a6c842f480f7bf99ac9640fbba9 Mon Sep 17 00:00:00 2001
From: northline-lab <northline-lab@users.noreply.github.com>
Date: Sat, 30 May 2026 17:37:33 +0000
Subject: [PATCH] test: add trace writer unit coverage

Add focused unit tests for TraceWriter behavior:

- parent directory and empty trace file creation
- state/event/payload JSONL fields
- default empty payload handling
- append ordering across multiple writes
- non-ASCII payload round-trip

Verification:
- UV_CACHE_DIR=/tmp/uv-cache UV_PROJECT_ENVIRONMENT=/tmp/contribarena-uv-venv uv run --extra dev pytest -q tests/unit/test_trace_writer.py
- UV_CACHE_DIR=/tmp/uv-cache UV_PROJECT_ENVIRONMENT=/tmp/contribarena-uv-venv uv run --extra dev ruff check tests/unit/test_trace_writer.py
---
 tests/unit/test_trace_writer.py | 50 +++++++++++++++++++++++++++++++--
 1 file changed, 48 insertions(+), 2 deletions(-)

diff --git a/tests/unit/test_trace_writer.py b/tests/unit/test_trace_writer.py
index 5b79f5c..d5df63b 100644
--- a/tests/unit/test_trace_writer.py
+++ b/tests/unit/test_trace_writer.py
@@ -4,23 +4,69 @@
 import tempfile
 import unittest
 from pathlib import Path
+from typing import Any
 
 from contribarena.trace import TraceWriter
 
 
+def _read_events(path: Path) -> list[dict[str, Any]]:
+    return [json.loads(line) for line in path.read_text(encoding="utf-8").splitlines()]
+
+
 class TraceWriterTest(unittest.TestCase):
+    def test_creates_parent_directory_and_trace_file(self) -> None:
+        with tempfile.TemporaryDirectory() as tmp:
+            path = Path(tmp) / "nested" / "trace.jsonl"
+
+            TraceWriter(path, "run-1")
+
+            self.assertTrue(path.parent.is_dir())
+            self.assertEqual("", path.read_text(encoding="utf-8"))
+
     def test_writes_jsonl_event(self) -> None:
         with tempfile.TemporaryDirectory() as tmp:
             path = Path(tmp) / "trace.jsonl"
             writer = TraceWriter(path, "run-1")
             writer.write("run_started", "run.started", {"ok": True})
 
-            [line] = path.read_text(encoding="utf-8").splitlines()
-            event = json.loads(line)
+            [event] = _read_events(path)
             self.assertEqual("run-1", event["run_id"])
+            self.assertEqual("run_started", event["state"])
             self.assertEqual("run.started", event["event"])
             self.assertTrue(event["payload"]["ok"])
 
+    def test_defaults_missing_payload_to_empty_object(self) -> None:
+        with tempfile.TemporaryDirectory() as tmp:
+            path = Path(tmp) / "trace.jsonl"
+            writer = TraceWriter(path, "run-1")
+
+            writer.write("tool_started", "tool.started")
+
+            [event] = _read_events(path)
+            self.assertEqual({}, event["payload"])
+
+    def test_appends_events_in_write_order(self) -> None:
+        with tempfile.TemporaryDirectory() as tmp:
+            path = Path(tmp) / "trace.jsonl"
+            writer = TraceWriter(path, "run-1")
+
+            writer.write("first", "event.first", {"index": 1})
+            writer.write("second", "event.second", {"index": 2})
+
+            events = _read_events(path)
+            self.assertEqual(["event.first", "event.second"], [event["event"] for event in events])
+            self.assertEqual([1, 2], [event["payload"]["index"] for event in events])
+
+    def test_round_trips_non_ascii_payload(self) -> None:
+        with tempfile.TemporaryDirectory() as tmp:
+            path = Path(tmp) / "trace.jsonl"
+            writer = TraceWriter(path, "run-1")
+
+            writer.write("message", "message.created", {"text": "café"})
+
+            [event] = _read_events(path)
+            self.assertEqual("café", event["payload"]["text"])
+
 
 if __name__ == "__main__":
     unittest.main()