ean rails validator

ean_validator.rb

class EANValidator < ActiveModel::EachValidator

  def validate_each(record, attribute, value)
    unless ean_valid?(value)
      record.errors[attribute] << (options[:message] || :bad_ean)
    end
  end

  def valid?(ean)
    return false unless ean.length == 13
    return false if ean.match(/[^\d]/)
    ean_array = ean.chars.map(&:to_i)
    verifier_digit = ean_array.pop

    result = ean_array.each_with_index.reduce(0) do |sum, (value, index)|
      sum += index.odd? ? (value * 3) : value
    end
    calculated_verifier_digit = result - (result % 10)

    verifier_digit == calculated_verifier_digit
  end
end

ean_validator_spec.rb

require 'rails_helper'

describe EANValidator do

  subject(:validator) { EANValidator.new({attributes: { foo: :bar}}) }

  describe '#validate_each' do

    let!(:product) { double 'product' }

    before do
      allow(product).to receive(:errors).and_return([])
      allow(product.errors).to receive('[]').and_return([])
    end

    context 'valid ean' do
      it do
        expect(product).to_not receive(:errors)
        validator.validate_each(product, 'ean', '7891627314051')
      end
    end

    context 'invalid ean' do
      it do
        expect(product).to receive(:errors)
        validator.validate_each(product, 'ean', '1234567890987')
      end
    end
  end

  describe '.valid?' do
    subject(:validator) { EANValidator }

    context 'valid ean' do
      ['7891627314051', '9311960043718'].each do |ean|
        it { expect(validator.valid?(ean)).to be_truthy }
      end
    end

    context 'invalid ean' do
      it { expect(validator.valid?('7898490000482')).to be_falsey }
    end
  end
end