public void RetvalAsync()
        {
            var handler = CreateClass("MyService", "RetvalAsync")(null);

            service.RetvalAsync().Returns(Task.FromResult(123456789));

            var expectedData = new byte[4];

            fixed(byte *pData = expectedData)
            {
                *(int *)pData = 123456789;
            }

            var resultingTask = handler.Handle(service, null, 0);

            Assert.That(resultingTask.Result, Is.EqualTo(expectedData));
        }