Add validation to User model
Add length validation to User model
Add format validation to User model
Add uniquness validation to User model
Add uniquness validation to Database
Add password_digest column to Users
Add has_secure_password to User model and comment out it

For tutorial
Add has_secure_password test
6.5 Exercise 1 : Test email address with mixed case
6.5 Exercise 2 : Use email.downcase!
6.5 Exercise 3 : Improve email regexp
Add debug display
Create a mock for displaying user
Bundle FactoryGirl
Use gravatar image in user profile page
Add sign up test
Add signup form
Add create to user_controller
Support Strong Parameters
Error message of user registration