Unit testing for Validation Attributes in c#

I was trying to do unit testing for validations on c# models using Validator but it is not working with NewtonSoft attributes. Can someone help me with this?

var searchController = new SearchController();
            var requestModel = new RequestModel
            {
                Id = "23456",
                MobileNumber = "9876543210"
            };
            var results = new List<ValidationResult>();
            var context = new ValidationContext(requestModel, null, null);
            var isvalid = Validator.TryValidateObject(requestModel, context, results,true);
            Assert.IsFalse(isvalid);