From 01150adba3f6db1b17ad86dc45ac3f70d13f8f8d Mon Sep 17 00:00:00 2001
From: Nalu Tripician <27316859+NaluTripician@users.noreply.github.com>
Date: Thu, 19 Mar 2026 13:00:43 -0700
Subject: [PATCH] [Internal] Tests: Fixes AppCancellationDuringHedging with
 deterministic synchronization

Replaces timing-dependent Task.Delay cancellation pattern with
deterministic TaskCompletionSource + ct.Register() approach.
Previously used 10ms threshold + 15ms cancel delay (5ms margin),
which was unreliable on loaded CI agents.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
---
 .../AvailabilityStrategyUnitTests.cs          | 23 ++++++++-----------
 1 file changed, 10 insertions(+), 13 deletions(-)

diff --git a/Microsoft.Azure.Cosmos/tests/Microsoft.Azure.Cosmos.Tests/AvailabilityStrategyUnitTests.cs b/Microsoft.Azure.Cosmos/tests/Microsoft.Azure.Cosmos.Tests/AvailabilityStrategyUnitTests.cs
index 8123290a06..e2d91daa3c 100644
--- a/Microsoft.Azure.Cosmos/tests/Microsoft.Azure.Cosmos.Tests/AvailabilityStrategyUnitTests.cs
+++ b/Microsoft.Azure.Cosmos/tests/Microsoft.Azure.Cosmos.Tests/AvailabilityStrategyUnitTests.cs
@@ -281,8 +281,8 @@ public async Task AppCancellationDuringHedging_DoesNotSpawnNewHedgeRequests()
         {
             // Arrange
             CrossRegionHedgingAvailabilityStrategy availabilityStrategy = new CrossRegionHedgingAvailabilityStrategy(
-                threshold: TimeSpan.FromMilliseconds(10),
-                thresholdStep: TimeSpan.FromMilliseconds(10));
+                threshold: TimeSpan.FromMilliseconds(100),
+                thresholdStep: TimeSpan.FromMilliseconds(100));
 
             using RequestMessage request = CreateReadRequest();
             using CosmosClient mockCosmosClient = CreateMockClientWithRegions(3);
@@ -296,19 +296,16 @@ public async Task AppCancellationDuringHedging_DoesNotSpawnNewHedgeRequests()
 
                 if (callNumber == 1)
                 {
-                    // First request: cancel the app token after a brief delay
+                    // First request: cancel the app token immediately
                     // This simulates an e2e timeout scenario
-                    _ = Task.Delay(15).ContinueWith(_ => appCts.Cancel());
+                    appCts.Cancel();
+                }
 
-                    // Then wait - this will be cancelled
-                    try
-                    {
-                        await Task.Delay(TimeSpan.FromSeconds(30), ct);
-                    }
-                    catch (OperationCanceledException)
-                    {
-                        throw;
-                    }
+                // All requests block deterministically until cancelled via the token
+                TaskCompletionSource<ResponseMessage> tcs = new TaskCompletionSource<ResponseMessage>();
+                using (ct.Register(() => tcs.TrySetCanceled(ct)))
+                {
+                    await tcs.Task;
                 }
 
                 return new ResponseMessage(HttpStatusCode.OK);