Ensure for before_action

It’s common to have code like this in controllers:

class HomeController < ApplicationController
  before_action :ensure_car_exists, only: [:index]
end

Note that, in this case, the method name is ensure_car_exists. Another possible name for it could be verify_car_exists.

Both names are good names - however, we have adopted a convention that such method names should start with ensure_.

Another example

class HomeController < ApplicationController
  before_action :authenticate_admin
end

:authenticate_admin is a perfectly valid name. However, we prefer before_action :ensure_user_is_admin.