yoba_validator.rb

# app/models/document.rb

class Person < ActiveRecord::Base
  validate &PassportValidator
end

# lib/yoba_validator.rb

class YobaValidator < SimpleDelegator
  include ActiveModel::Validations

  def validate
    super
    errors.each do |f, e|
      @delegate_sd_obj.errors.add(f, e)
    end
  end

  def self.to_proc
    kl = self
    -> (obj) { kl.new(obj).validate }
  end
end

# app/validators/passport_validator.rb

class PassportValidator < YobaValidator
  SERIES_REGEX = /.+/
  validates :passport, format: { with: SERIES_REGEX }
end

# spec/validators/passport_validator_spec.rb

require 'spec_helper'

describe PassportValidator do
  subject { described_class.new(obj) }

  context 'with valid series' do
    let(:obj) { double(passport: 'foo') }

    it { is_expected.to be_valid }
  end

  context 'with invalid series' do
    let(:obj) { double(passport: '') }

    it { is_expected.not_to be_valid }
  end
end