NameError: uninitialized constant ApplicationHelperTest::Fill_IN

I get this error message when I add the last test in this code from Ruby on Rails Tutorial, from listing 6.11 and 6.12 and then run the bundle exec rake test Listing 6.13 I am running Linux Xubuntu

1) Error: ApplicationHelperTest#test_full_title_helper: NameError: uninitialized constant ApplicationHelperTest::FILL_IN test/helpers/application_helper_test.rb:5:in `block in '

When I remove the email validation the test passes.

test/models/user_test.rb

require 'test_helper'

class UserTest < ActiveSupport::TestCase
  def setup
    @user = User.new(name: "Example User", email: "user@example.com")
  end

  test "should be valid" do
    assert @user.valid?
  end

  test "name should be present" do
    @user.name = ""
    assert_not @user.valid?
  end

  test "email should be present" do
    @user.email = "     "
    assert_not @user.valid?
  end  
end

app/models/user.rb

class User < ActiveRecord::Base
  validates :name,  presence: true
  validates :email, presence: true
end

I think it must have something to do with the Application Helper. this is the code in the helper:

require 'test_helper'

class ApplicationHelperTest < ActionView::TestCase

  test "full title helper" do
    assert_equal full_title,         FILL_IN
    assert_equal full_title("Help"), FILL_IN
  end
end