##the error message:
Spec::Mocks::MockExpectationError in 'UsersController responding to POST create with valid params should redirect to the created user'
Mock 'User_1038' received unexpected message :screen_name with (no args)
C:/projects/Learning/app/controllers/users_controller.rb:47:in `create'
C:/projects/Learning/app/controllers/users_controller.rb:45:in `create'
./spec/controllers/users_controller_spec.rb:85:

## the spec:
describe UsersController do

  def mock_user(stubs={})
    @mock_user ||= mock_model(User, stubs)
  endwhat
...
  describe "responding to POST create" do

    describe "with valid params" do

      it "should expose a newly created user as @user" do
        User.should_receive(:new).with({'these' => 'params'}).and_return(mock_user(:save => true))
        post :create, :user => {:these => 'params'}
        assigns(:user).should equal(mock_user)
      end

      it "should redirect to the created user" do
        User.stub!(:new).and_return(mock_user(:save => true))
        post :create, :user => {}
        response.should redirect_to(user_url(mock_user))
      end

    end

##user model:
require 'digest/sha1'
class User < ActiveRecord::Base
  SCREEN_NAME_MIN_LENGTH =4
  SCREEN_NAME_MAX_LENGTH = 20
  EMAIL_MIN_LENGTH = 6
  EMAIL_MAX_LENGTH = 50
  EMAIL_SIZE = 30
  SCREEN_NAME_SIZE = 20
  PASSWORD_MIN_LENGTH =5
  PASSWORD_MAX_LENGTH = 50
  PASSWORD_SIZE = 20
  validates_uniqueness_of :screen_name
  validates_length_of :screen_name, :within =>SCREEN_NAME_MIN_LENGTH..SCREEN_NAME_MAX_LENGTH
  validates_length_of :email, :within => EMAIL_MIN_LENGTH..EMAIL_MAX_LENGTH
  validates_presence_of :email,:screen_name
  validates_format_of :screen_name, :with =>/^[A-Z0-9_]*$/i, :message =>"must contain only letters, numbers, and underscores"
  validates_format_of :email, :with =>/^[A-Z0-9._%-+]+@([A-Z0-9-]+\.)+[A-Z]{2,4}$/i, :message => "must be a valid e-mail address"
  validates_confirmation_of :password
  attr_accessor :password_confirmation


  def validate
    if self.hashed_password.nil?
      errors.add_to_base("The password needs to be between #{PASSWORD_MIN_LENGTH} and #{PASSWORD_MAX_LENGTH} characters.")
    end
  end

  #this returns the virtual attribute password
  def password
    @password
  end

  #This ensures that the password is long enough and assigns it or it returns nil
  def password=(pass)
    if (PASSWORD_MIN_LENGTH..PASSWORD_MAX_LENGTH) === pass.length #I bypassed this to make sure that it is working
       @password = pass
       self.salt = create_salt
       self.hashed_password = encrypt_password( pass, self.salt)
    else
      return nil
    end
    self.hashed_password
  end

  #this returns the user if the password is correct or it returns nil
  def self.authenticate( login, password)
    bob = find_by_screen_name( login)
    bob && bob.hashed_password ==  encrypt_password( password, bob.salt)? bob: nil
  end

  protected

  #This function takes a password, salts it, stretches it, and returns it.
  #This depends on  SITE_KEY  and STRETCH_ITERATIONS  being set.
  #I don't know if this is implemented securely.
  def encrypt_password(password, salt)
   encrypted_password = SITE_KEY
   STRETCH_ITERATIONS.times do
       encrypted_password = Digest::SHA1.hexdigest(password + '::' + encrypted_password  + '::' + salt + '::' + SITE_KEY)
   end
   encrypted_password
  end

  #this returns a new salt
  def create_salt
    self.object_id.to_s + rand.to_s
  end
end