improved timeout after memory usage

Tests/MQTTnet.Core.Tests/ExtensionTests.cs

@@ -1,4 +1,5 @@
 using System;
+using System.Linq;
 using System.Threading.Tasks;
 using Microsoft.VisualStudio.TestTools.UnitTesting;
 using MQTTnet.Core.Exceptions;
@@ -67,5 +68,23 @@ namespace MQTTnet.Core.Tests
                 Assert.IsTrue(e.InnerException is IndexOutOfRangeException);
             }
         }
+
+        [TestMethod]
+        public async Task TimeoutAfterMemoryUsage()
+        {
+            var tasks = Enumerable.Range(0, 100000)
+                .Select(i => Task.Delay(TimeSpan.FromMilliseconds(1)).TimeoutAfter(TimeSpan.FromMinutes(1)));
+
+            await Task.WhenAll( tasks );
+            AssertIsLess( 3_000_000, GC.GetTotalMemory( true ) );
+        }
+
+        private void AssertIsLess( long bound, long actual )
+        {
+            if ( bound < actual )
+            {
+                Assert.Fail( $"value must be less than {bound:N0} but is {actual:N0}" );
+            }
+        }
     }
 }