public void AddedMessagesCanBeRetrieved()
        {
            var queue    = new InMemoryQueue();
            var message1 = new object();
            var message2 = new object();
            var message3 = new object();

            var index1 = queue.AddMessage(new object(), null, message1);
            var index2 = queue.AddMessage(null, new object(), message2);
            var index3 = queue.AddMessage(null, new object(), message3);

            queue.GetMessage(index1).Should().Be(message1);
            queue.GetMessage(index2).Should().Be(message2);
            queue.GetMessage(index3).Should().Be(message3);
        }