You can create a new Devise user simply by creating a new user model (see https://github.com/plataformatec/devise/wiki/How-To:-Manage-users-through-a-CRUD-interface)
@user = User.new(:email => 'test@example.com', :password => 'password', :password_confirmation => 'password')
@user.save
To sign in your newly created user, use sign_in @user