var controller = new CustomerController(_customerService.Object);
var newModel = new CreateModel();

var validationContext = new ValidationContext(newModel, null, null);
var validationResults = new List<ValidationResult>();
Validator.TryValidateObject(newModel, validationContext, validationResults, true);
foreach (var validationResult in validationResults)
{
	controller.ModelState.AddModelError(validationResult.MemberNames.FirstOrDefault() ?? string.Empty, validationResult.ErrorMessage);
}

Assert.AreEqual(4, controller.ModelState.ErrorCount);