gh-157157: Make test_taskgroup_cancel_keeps_outer_cancellation deterministic (#157158)

Author: iamsharduld

Lib/test/test_asyncio/test_taskgroups.py

@@ -1200,11 +1200,17 @@ async def child(tg):
 
     async def test_taskgroup_cancel_keeps_outer_cancellation(self):
         # gh-155433: any cancellation from outside the group must propagate.
+        cancelling = asyncio.Event()
+        release = asyncio.Event()
+
         async def child():
             try:
                 await asyncio.sleep(10)
             finally:
-                await asyncio.sleep(0.1)
+                # The group is cancelling: it has cancelled its parent task
+                # and is waiting for this task to finish.
+                cancelling.set()
+                await release.wait()
 
         async def body():
             async with asyncio.TaskGroup() as tg:
@@ -1213,8 +1219,9 @@ async def body():
                 tg.cancel()
 
         task = asyncio.create_task(body())
-        await asyncio.sleep(0.01)
+        await cancelling.wait()
         task.cancel('message')
+        release.set()
         with self.assertRaises(asyncio.CancelledError) as cm:
             await task
         self.assertEqual('message', cm.exception.args[0])