Model:

  attr_accessor :password, :terms_of_service

  validates_acceptance_of :terms_of_service, :on => :create, :allow_nil => false

Test (failing):

  def test_should_create_user
    assert_difference 'User.count' do
      user = create_user
      assert !user.new_record?, "#{user.errors.full_messages.to_sentence}"
    end
  end

protected

    def create_user(options = {})
      User.create({ :login => 'quire', :email => 'quire@example.com', :password => 'quire', :password_confirmation => 'quire', :terms_of_service => "1" }.merge(options))
    end