Add (possibly flaky) test for slow handler logging

src/textual/message_pump.py

@@ -11,7 +11,6 @@
 from __future__ import annotations
 
 import asyncio
-import os
 import threading
 from asyncio import CancelledError, Queue, QueueEmpty, Task, create_task
 from contextlib import contextmanager
@@ -207,7 +206,7 @@ def message_queue_size(self) -> int:
         return self._message_queue.qsize()
 
     @property
-    def is_dom_root(self):
+    def is_dom_root(self) -> bool:
         """Is this a root node (i.e. the App)?"""
         return False
 
@@ -264,7 +263,7 @@ def log(self) -> Logger:
         Returns:
             A logger.
         """
-        return self.app._logger
+        return self.app.log
 
     def _attach(self, parent: MessagePump) -> None:
         """Set the parent, and therefore attach this node to the tree.
@@ -669,11 +668,11 @@ async def _dispatch_message(self, message: Message) -> None:
             # Allow apps to treat events and messages separately
             if isinstance(message, Event):
                 await self.on_event(message)
-            elif "debug" in self.app.features:
+            elif self.app.debug:
                 start = perf_counter()
                 await self._on_message(message)
                 if perf_counter() - start > SLOW_THRESHOLD / 1000:
-                    log.warning(
+                    self.log.warning(
                         f"method=<{self.__class__.__name__}."
                         f"{message.handler_name}>",
                         f"Took over {SLOW_THRESHOLD}ms to process.",

tests/test_message_pump.py

@@ -1,5 +1,8 @@
+from unittest.mock import Mock
+
 import pytest
 
+from textual import Logger
 from textual._dispatch_key import dispatch_key
 from textual.app import App, ComposeResult
 from textual.errors import DuplicateKeyHandlers
@@ -169,3 +172,35 @@ def on_button_pressed(self, event: Button.Pressed) -> None:
     async with app.run_test() as pilot:
         await pilot.click(MyButton)
         assert app_button_pressed
+
+
+async def test_slow_handler(monkeypatch):
+    """Test that a slow handler results in a logged warning."""
+
+    log_mock = Mock()
+    monkeypatch.setenv("TEXTUAL_SLOW_THRESHOLD", "200")
+
+    class SlowHandlerApp(App[None]):
+        def compose(self) -> ComposeResult:
+            yield Button("Press me")
+
+        async def on_button_pressed(self, event: Button.Pressed) -> None:
+            import time
+
+            time.sleep(0.5)
+
+        @property
+        def log(self) -> Logger:
+            return log_mock
+
+        @property
+        def debug(self) -> bool:
+            return True
+
+    app = SlowHandlerApp()
+    async with app.run_test() as pilot:
+        await pilot.click(Button)
+        warning_logs = log_mock.warning.call_args_list
+        assert len(warning_logs) == 1
+        assert "method=<SlowHandlerApp.on_button_pressed>" in warning_logs[0][0]
+        assert "consider using a worker" in warning_logs[0][0][2]