redirect_to rspec test error

gistfile1.rb

class UsersController < ApplicationController
  def new
    @user = User.new
    @title = "Sign up"
  end

  def create
    @user = User.new(params[:user])
    if @user.save
      redirect_to login_url, :notice => "Signed up!"
    else
      @title = "Sign up"
      render :new
    end
  end
end

describe "Users" do
  describe "signup" do
    describe "success" do
      it "should make a new user" do
        lambda do
          visit signup_path
          fill_in "Username",         :with => "foobar"
          fill_in "Email",        :with => "foo@bar.com"
          fill_in "Password",     :with => "foobar123"
          fill_in "Password confirmation", :with => "foobar123"
          click_button
          response.should redirect_to(login_path)
          response.should have_selector('div.flash.notice',
                                        :content => "Signed up!")
        end.should change(User, :count).by(1)
      end
    end
  end
end

test fails saying

  1) Users signup success should make a new user
     Failure/Error: response.should redirect_to(login_path)
       Expected response to be a <:redirect>, but was <200>