private ValidationMessage LessThan <TProp>(
TProp value,
TProp valueToCompare,
IComparer comparer = null,
ValidationMessageType validationMessageType = ValidationMessageType.Error)
where TProp : IComparable <TProp>
{
var lessThanValidator = new LessThanValidator <TestValidatableObject, TProp>(_ => valueToCompare, comparer, validationMessageType);
var context = new ValidationContext <TestValidatableObject, TProp>(null, nameof(TestValidatableObject.Number), null, value);
var validationMessage = lessThanValidator.ValidateProperty(context).FirstOrDefault();
return(validationMessage);
}