email validation

app/models/account.rb

@@ -5,5 +5,5 @@ class Account < ApplicationRecord
   validates :username, presence: true
   validates :password, presence: true
   validates :home_folder, presence: true
-  validates :contact_email, presence: true
+  validates :contact_email, presence: true, email_format: true
 end

app/validators/email_format_validator.rb

@@ -0,0 +1,13 @@
+# frozen_string_literal: true
+class EmailFormatValidator < ActiveModel::EachValidator
+  def validate_each(record, attribute, value)
+    # EMAIL regex test
+    # (comma seperated) [any word combo] AT [any word combo] DOT [2 or more]
+    # me@no.yes.x == invalid
+    # some.thing+two@sub.domain.name == valid
+    results = value.to_s.split(',').map do |v|
+      (v.strip =~ /^([\w\.%\+\-]+)@([\w\-]+\.)+([\w]{2,})$/i) || v.strip.blank?
+    end
+    record.errors[attribute] << (options[:message] || "is not formatted properly") if results.include?(false)
+  end
+end

test/test_helpers/email_validatable.rb

@@ -0,0 +1,6 @@
+# frozen_string_literal: true
+class EmailValidatable
+  include ActiveModel::Validations
+  attr_accessor :email
+  validates :email, email_format: true
+end

test/validators/email_format_validator_test.rb

@@ -0,0 +1,27 @@
+# frozen_string_literal: true
+require 'test_helper'
+class EmailFormatValidatorTest < ActiveSupport::TestCase
+  test "tld length" do
+    obj = EmailValidatable.new
+    obj.email = "me@no.yes.x"
+    refute obj.valid?, 'allowed single length tld'
+    obj.email = "me@no.yes.co"
+    assert obj.valid?, 'did not allow tld length 2'
+    obj.email = "me@no.yes.com"
+    assert obj.valid?, 'did not allow tld length 3'
+    obj.email = "me@no.yes.commets"
+    assert obj.valid?, 'did not allow tld length > 3'
+  end
+  test "can handle comma seperated addresses" do
+    obj = EmailValidatable.new
+    obj.email = "me@no.yes, me@yes.no"
+    assert obj.valid?, 'did not allow multiple address [comma seperated]'
+  end
+  test "provides proper error message" do
+    obj = EmailValidatable.new
+    obj.email = "this is a bad email address"
+    obj.valid?
+    refute obj.errors.messages.empty?, 'needs an error message'
+    assert_match(/not formatted properly/, obj.errors.messages[:email].join)
+  end
+end