fix : await 버그 픽스

ClientTester/EchoClientTester/EchoDummyService/EchoDummyClientService.cs

@@ -72,6 +72,15 @@ public class EchoDummyClientService
 
     private async Task SendLoopAsync(CancellationToken ct)
     {
+        try
+        {
+            await Task.Delay(500, ct);
+        }
+        catch (OperationCanceledException)
+        {
+            return;
+        }
+
         int tick = 0;
 
         while (!ct.IsCancellationRequested)
@@ -140,6 +149,7 @@ public class EchoDummyClientService
                 totalAvgRtt += c.AvgRttMs;
                 rttClientCount++;
             }
+
             if (c.peer != null)
             {
                 connected++;