public void GivenAQueueWithThreeUsers_EnsureExpectedOrderWhenPopping()
        {
            var queue = new UserQueue();

            queue.PushUserToQueue(Guid.NewGuid(), "Dan");
            queue.PushUserToQueue(Guid.NewGuid(), "Bob");
            queue.PushUserToQueue(Guid.NewGuid(), "Fred");
            queue.PopUserFromQueue().Should().BeEquivalentTo("Dan");
            queue.PopUserFromQueue().Should().BeEquivalentTo("Bob");
            queue.PopUserFromQueue().Should().BeEquivalentTo("Fred");
            queue.PopUserFromQueue().Should().BeNull();
        }
        public void GivenAnEmptyQueue_WhenPushingNewUserToQueue_ThenPoppingUserShouldReturnThatUser()
        {
            var queue = new UserQueue();

            queue.PushUserToQueue(Guid.NewGuid(), "Dan");
            queue.PopUserFromQueue().Should().BeEquivalentTo("Dan");
        }