@user = User.new(:email => 'test@example.com', :password => 'password', :password_confirmation => 'password')
@user.save

@user = User.new(:email => 'test@example.com',
                 :password => 'password',
                 :password_confirmation => 'password')
# This will save the user in db with fields for devise
sign_in @user
# :bypass is set to ignore devise related callbacks and only save the
# user into session.
sign_in @user, :bypass => true

config/routes.rb

devise_for :users

devise_for :users, :path_prefix =>'auth'