validates!

This method is used to define validations that cannot be corrected by end users and are considered exceptional. So each validator defined with bang or :strict option set to true will always raise ActiveModel::StrictValidationFailed instead of adding error when validation fails. See validates for more information about the validation itself.

class Person
  include ActiveModel::Validations

  attr_accessor :name
  validates! :name, presence: true
end

person = Person.new
person.name = ''
person.valid?
# => ActiveModel::StrictValidationFailed: Name can't be blank