login_app.rb

require 'rubygems'
require "sinatra"

enable :sessions
#use Rack::Session::Cookie
#use Rack::Session::Pool

  get '/' do
    if session[:username]
      "hi, #{session[:username]}"
    else
      "please log in: <form action='/login' method='get'><input name='username'><input type='submit'></form>"
    end
  end

  get '/login' do
    session[:username] = params[:username]
    "logged in as #{session[:username]}"
  end

  get '/logout' do
    old_user = session[:username]
    session[:username] = nil
    "logged out #{old_user}"
  end

login_app_test.rb

ENV['RACK_ENV'] = 'test' 

require 'rubygems'
require 'rack'
require 'test/unit'
require "rack/test"

require 'login_app'

class AppTest < Test::Unit::TestCase
  include Rack::Test::Methods

  def app
    Sinatra::Application
  end
  
  def session
    last_request.env['rack.session']
  end
  
  def test_login
    get '/login', :username => "barack"
    assert_equal "logged in as barack", last_response.body
    assert_equal "barack", session[:username]
  end

  def test_logout
    get '/login', :username => "barack"
    assert_equal "barack", session[:username]

    get '/logout'
    assert_nil session[:username]
    assert_equal "logged out barack", last_response.body
  end

  def test_logout_with_session_passed_explicitly
    get '/logout', {}, 'rack.session' => {:username => 'barry'}
    assert_nil session[:username]
    assert_equal "logged out barry", last_response.body
  end

  def test_main_page
    get '/login', :username => "barack"
    assert_equal "barack", session[:username]
    assert_equal "logged in as barack", last_response.body

    get '/'
    assert last_response.body =~ /hi, barack/

    get '/logout'
    assert_equal "logged out barack", last_response.body
    assert_nil session[:username]

    get '/'
    assert last_response.body =~ /please log in/
  end

end