A Simple Example of Building a Custom Validator - for my talk "Validate Me!"

validate_me.rb

# frozen_string_literal: true

require "bundler/inline"

gemfile(true) do
  source "https://rubygems.org"

  gem "rails"
  # If you want to test against edge Rails replace the previous line with this:
  # gem "rails", github: "rails/rails", branch: "main"
end

require "active_support"
require "active_model"
require "active_support/core_ext/object/blank"
require "minitest/autorun"

class MeValidator < ActiveModel::EachValidator
  def validate_each(record, attr_name, value)
    record.errors.add(attr_name, 'is not me?!', **options) unless ['me', 'chael', 'Rachael'].include? value
  end
end

def validates_me_of(*attr_names)
  validates_with MeValidator, _merge_attributes(attr_names)
end

class ExampleModel
  include ActiveModel::API

  attr_accessor :the_best

  validates_me_of :the_best
end

class BugTest < Minitest::Test
  def test_validator_registered
    # assert_includes(ExampleModel._validators, '')
  end

  def test_validation_passes
    example = ExampleModel.new(the_best: 'me')
    assert(example.valid?)
    assert_empty(example.errors)
  end

  def test_validation_fails
    example = ExampleModel.new(the_best: 'not me')
    assert_empty(example.errors) # No errors until valid? is called
    assert_equal(example.valid?, false)
    assert_includes(example.errors.full_messages, 'The best is not me?!')
  end
end