Add `annotate` gem, User model and migrate database
Add sensible tests for user
Add tests for user name and email presence
Add test checking user name length
Add test checking email validation
Add test checking if email is not duplicated
Add index on the email column to make finding by email faster and ensure email uniqueness in database
Add password column in database and test for it
Make test passed
Add tests for password authentication and make all the tests work
Add a test for the email downcasing
Alternative way to save email in lowercase