New unit test to verify CompleteWithinAsync behaves correctly in an a…

…ssertion scope (#2033)

* Add new unit test to verify #2004

* fix test name

Tests/FluentAssertions.Specs/Specialized/TaskOfTAssertionSpecs.cs

@@ -143,6 +143,28 @@ public async Task When_task_completes_late_it_should_fail()
             await action.Should().ThrowAsync<XunitException>();
         }
 
+        [Fact]
+        public async Task When_task_completes_late_it_in_assertion_scope_should_fail()
+        {
+            // Arrange
+            var timer = new FakeClock();
+            var taskFactory = new TaskCompletionSource<int>();
+
+            // Act
+            Func<Task> action = () =>
+            {
+                Func<Task<int>> func = () => taskFactory.Task;
+
+                using var _ = new AssertionScope();
+                return func.Should(timer).CompleteWithinAsync(100.Milliseconds());
+            };
+
+            timer.Complete();
+
+            // Assert
+            await action.Should().ThrowAsync<XunitException>();
+        }
+
         [Fact]
         public async Task When_task_consumes_time_in_sync_portion_it_should_fail()
         {