validate_only (Validatable)

        # File lib/validatable_instance_methods.rb, line 49
    49:   def validate_only(key)
    50:     validation_name, attribute_name = key.split("/")
    51:     validation_name = validation_name.split("_").collect{|word| word.capitalize}.join
    52:     validation_key = "#{self.class.name}/Validatable::Validates#{validation_name}/#{attribute_name}"
    53:     validation = self.class.all_validations.find { |validation| validation.key == validation_key }
    54:     raise ArgumentError.new("validation with key #{validation_key} could not be found") if validation.nil?
    55:     errors.clear
    56:     run_validation(validation)
    57:   end