refactor: migrate echo example test to use Trio for process handling

tests/examples/test_echo_thin_waist.py

@@ -1,51 +1,65 @@
-import asyncio
 import contextlib
-import subprocess
 import sys
-import time
 from pathlib import Path
 
 import pytest
+import trio
 
 # This test is intentionally lightweight and can be marked as 'integration'.
-# It ensures the echo example runs and prints the new Thin Waist lines.
+# It ensures the echo example runs and prints the new Thin Waist lines using Trio primitives.
 
 EXAMPLES_DIR = Path(__file__).parent.parent.parent / "examples" / "echo"
 
 
-@pytest.mark.timeout(20)
-def test_echo_example_starts_and_prints_thin_waist(monkeypatch, tmp_path):
-    # We run: python examples/echo/echo.py -p 0
+@pytest.mark.trio
+async def test_echo_example_starts_and_prints_thin_waist() -> None:
     cmd = [sys.executable, str(EXAMPLES_DIR / "echo.py"), "-p", "0"]
-    proc = subprocess.Popen(
-        cmd,
-        stdout=subprocess.PIPE,
-        stderr=subprocess.STDOUT,
-        text=True,
-    )
-    assert proc.stdout is not None
 
     found_selected = False
     found_interfaces = False
-    start = time.time()
 
-    try:
-        while time.time() - start < 10:
-            line = proc.stdout.readline()
-            if not line:
-                time.sleep(0.1)
-                continue
-            if "Selected binding address:" in line:
-                found_selected = True
-            if "Available candidate interfaces:" in line:
-                found_interfaces = True
-            if "Waiting for incoming connections..." in line:
-                break
-    finally:
-        with contextlib.suppress(ProcessLookupError):
-            proc.terminate()
-        with contextlib.suppress(ProcessLookupError):
-            proc.kill()
+    # Use a cancellation scope as timeout (similar to previous 10s loop)
+    with trio.move_on_after(10) as cancel_scope:
+        # Start process streaming stdout
+        proc = await trio.open_process(
+            cmd,
+            stdout=trio.SUBPROCESS_PIPE,
+            stderr=trio.STDOUT,
+        )
+
+        assert proc.stdout is not None  # for type checkers
+        buffer = b""
+
+        try:
+            while not (found_selected and found_interfaces):
+                # Read some bytes (non-blocking with timeout scope)
+                data = await proc.stdout.receive_some(1024)
+                if not data:
+                    # Process might still be starting; yield control
+                    await trio.sleep(0.05)
+                    continue
+                buffer += data
+                # Process complete lines
+                *lines, buffer = buffer.split(b"\n") if b"\n" in buffer else ([], buffer)
+                for raw in lines:
+                    line = raw.decode(errors="ignore")
+                    if "Selected binding address:" in line:
+                        found_selected = True
+                    if "Available candidate interfaces:" in line:
+                        found_interfaces = True
+                    if "Waiting for incoming connections..." in line:
+                        # We have reached steady state; can stop reading further
+                        if found_selected and found_interfaces:
+                            break
+        finally:
+            # Terminate the long-running echo example
+            with contextlib.suppress(Exception):
+                proc.terminate()
+            with contextlib.suppress(Exception):
+                await trio.move_on_after(2)(proc.wait)  # best-effort wait
+            if cancel_scope.cancelled_caught:
+                # Timeout occurred
+                pass
 
     assert found_selected, "Did not capture Thin Waist binding log line"
     assert found_interfaces, "Did not capture Thin Waist interfaces log line"