test: add trace writer unit coverage

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()