public void TestParentTestMessage()
        {
            // When subscribing to ParentTest Event the appropriate handler will be invoked when
            //  child (descendant) message types are published.
            _bus.Subscribe <ParentTestEvent>(this);
            var parentTestEvent = new ParentTestEvent();

            _bus.Publish(parentTestEvent);
            AssertEx.IsOrBecomesTrue(() => _testEventCount == 0, msg: $"Expected 0 got {_testEventCount}");
            AssertEx.IsOrBecomesTrue(() => _parentTestEventCount == 1, msg: $"Expected 1 got {_parentTestEventCount}");
            AssertEx.IsOrBecomesTrue(() => _childTestEventCount == 0, msg: $"Expected 0 got {_childTestEventCount}");
            AssertEx.IsOrBecomesTrue(() => _grandChildTestEventCount == 0, msg: $"Expected 0 got {_grandChildTestEventCount}");

            _bus.Subscribe <ChildTestEvent>(this);
            var childTestEvent = new ChildTestEvent();

            _bus.Publish(childTestEvent);
            AssertEx.IsOrBecomesTrue(() => _testEventCount == 0, msg: $"Expected 0 got {_testEventCount}");
            AssertEx.IsOrBecomesTrue(() => _parentTestEventCount == 2, msg: $"Expected 2 got {_parentTestEventCount}");
            AssertEx.IsOrBecomesTrue(() => _childTestEventCount == 1, msg: $"Expected 1 got {_childTestEventCount}");
            AssertEx.IsOrBecomesTrue(() => _grandChildTestEventCount == 0, msg: $"Expected 0 got {_grandChildTestEventCount}");

            _bus.Subscribe <GrandChildTestEvent>(this);
            var grandChildTestEvent = new GrandChildTestEvent();

            _bus.Publish(grandChildTestEvent);
            AssertEx.IsOrBecomesTrue(() => _testEventCount == 0, msg: $"Expected 0 got {_testEventCount}");
            AssertEx.IsOrBecomesTrue(() => _parentTestEventCount == 3, msg: $"Expected 3 got {_parentTestEventCount}");
            AssertEx.IsOrBecomesTrue(() => _childTestEventCount == 2, msg: $"Expected 2 got {_childTestEventCount}");
            AssertEx.IsOrBecomesTrue(() => _grandChildTestEventCount == 1, msg: $"Expected 1 got {_grandChildTestEventCount}");
        }
 void IHandle <ChildTestEvent> .Handle(ChildTestEvent message) => Interlocked.Increment(ref _childTestEventCount);