private async void BeUniqueByName_Update_Not_Exists()
        {
            Mock <IProxyRepository> proxyRepository = new Mock <IProxyRepository>();

            proxyRepository.Setup(x => x.ByName(It.IsAny <string>())).Returns(Task.FromResult <Proxy>(null));
            var validator = new ApiProxyRequestModelValidator(proxyRepository.Object);

            await validator.ValidateUpdateAsync(default(string), new ApiProxyRequestModel());

            validator.ShouldNotHaveValidationErrorFor(x => x.Name, "A");
        }