Custom model validators in Rails

custom_model_validator.rb

#app/models/validators/valid_date_presence_validator.rb
 class ValidDatePresenceValidator < ActiveModel::EachValidator
  include DateHelpers

  def validate_each(record, attribute, value)
    unless valid_date? value
      record.errors[attribute] << ('is not a valid date')
    end
  end

end

#app/models/sponsorship.rb
 validates :start_date, valid_date_presence: true
 
#spec/models/sponsorship_spec.rb
#see custom Rspec matchers
 it { is_expected.to have_validation ValidDatePresenceValidator, :on => :start_date }