public async void SenderUserId_Update_Valid_Reference()
        {
            Mock <IMessageRepository> messageRepository = new Mock <IMessageRepository>();

            messageRepository.Setup(x => x.UserBySenderUserId(It.IsAny <int>())).Returns(Task.FromResult <User>(new User()));

            var validator = new ApiMessageRequestModelValidator(messageRepository.Object);
            await validator.ValidateUpdateAsync(default(int), new ApiMessageRequestModel());

            validator.ShouldNotHaveValidationErrorFor(x => x.SenderUserId, 1);
        }
        public async void Content_Update_length()
        {
            Mock <IMessageRepository> messageRepository = new Mock <IMessageRepository>();

            messageRepository.Setup(x => x.Get(It.IsAny <int>())).Returns(Task.FromResult(new Message()));

            var validator = new ApiMessageRequestModelValidator(messageRepository.Object);
            await validator.ValidateUpdateAsync(default(int), new ApiMessageRequestModel());

            validator.ShouldHaveValidationErrorFor(x => x.Content, new string('A', 129));
        }