Add distinction between error cases in TimerContext

CONTRIBUTORS.txt

@@ -140,6 +140,7 @@ Frederik Peter Aalund
 Gabriel Tremblay
 Gang Ji
 Gary Wilson Jr.
+Gary Yendell
 Gennady Andreyev
 Georges Dubus
 Greg Holt

aiohttp/helpers.py

@@ -658,7 +658,16 @@ def assert_timeout(self) -> None:
     def __enter__(self) -> BaseTimerContext:
         task = asyncio.current_task(loop=self._loop)
         if task is None:
-            raise RuntimeError("Timeout context manager should be used inside a task")
+            try:
+                asyncio.current_task()
+            except RuntimeError:
+                raise RuntimeError(
+                    "Timeout context manager should be used inside a task"
+                )
+            else:
+                raise RuntimeError(
+                    "Timeout context manager used in a task on a different event loop"
+                )
 
         if sys.version_info >= (3, 11):
             # Remember if the task was already cancelling

tests/test_helpers.py

@@ -6,6 +6,7 @@
 import weakref
 from math import ceil, modf
 from pathlib import Path
+from threading import Thread
 from typing import Dict, Iterator, Optional, Union
 from unittest import mock
 from urllib.request import getproxies_environment
@@ -403,11 +404,34 @@ async def task_with_timeout() -> None:
 
 
 def test_timer_context_no_task(loop: asyncio.AbstractEventLoop) -> None:
-    with pytest.raises(RuntimeError):
+    with pytest.raises(
+        RuntimeError, match="Timeout context manager should be used inside a task"
+    ):
         with helpers.TimerContext(loop):
             pass
 
 
+async def test_timer_context_wrong_event_loop() -> None:
+    loop = asyncio.get_running_loop()
+
+    async def use_timer(loop: asyncio.AbstractEventLoop = loop) -> None:
+        with pytest.raises(
+            RuntimeError,
+            match="Timeout context manager used in a task on a different event loop",
+        ):
+            with helpers.TimerContext(loop):
+                pass
+
+    other_loop = asyncio.new_event_loop()
+    thread = Thread(target=other_loop.run_forever)
+    thread.start()
+
+    asyncio.run_coroutine_threadsafe(use_timer(), other_loop).result(timeout=5)
+
+    other_loop.stop()
+    thread.join()
+
+
 async def test_weakref_handle(loop: asyncio.AbstractEventLoop) -> None:
     cb = mock.Mock()
     helpers.weakref_handle(cb, "test", 0.01, loop)