Fix flaky LongPolling tests (#14395)

Author: BrennanConroy

src/SignalR/common/testassets/Tests.Utils/VerifyNoErrorsScope.cs

@@ -1,4 +1,4 @@
-// Copyright (c) .NET Foundation. All rights reserved.
+// Copyright (c) .NET Foundation. All rights reserved.
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
 using System;
@@ -34,6 +34,32 @@ public void Dispose()
 
             var results = _sink.GetLogs().Where(w => w.Write.LogLevel >= LogLevel.Error).ToList();
 
+#if NETCOREAPP2_1 || NETCOREAPP2_2 || NET461
+            // -- Remove this code after 2.2 --
+            // This section of code is resolving test flakiness caused by a race in LongPolling
+            // The race has been resolved in version 3.0
+            // The below code tries to find is a DELETE request has arrived from the client before removing error logs associated with the race
+            // We do this because we don't want to hide any actual issues, but we feel confident that looking for DELETE first wont hide any real problems
+            var foundDelete = false;
+            var allLogs = _sink.GetLogs();
+            foreach (var log in allLogs)
+            {
+                if (foundDelete == false && log.Write.Message.Contains("Request starting") && log.Write.Message.Contains("DELETE"))
+                {
+                    foundDelete = true;
+                }
+
+                if (foundDelete)
+                {
+                    if ((log.Write.EventId.Name == "LongPollingTerminated" || log.Write.EventId.Name == "ApplicationError" || log.Write.EventId.Name == "FailedDispose")
+                        && log.Write.Exception?.Message.Contains("Reading is not allowed after reader was completed.") == true)
+                    {
+                        results.Remove(log);
+                    }
+                }
+            }
+#endif
+
             if (_expectedErrorsFilter != null)
             {
                 results = results.Where(w => !_expectedErrorsFilter(w.Write)).ToList();
@@ -64,4 +90,4 @@ public void Dispose()
             }
         }
     }
-}
+}