email validation

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