factory_bot allows you to define aliases to existing factories to make them easier to re-use. This could come in handy when, for example, your Post object has an author attribute that actually refers to an instance of a User class. While normally factory_bot can infer the factory name from the association name, in this case it will look for an author factory in vain. So, alias your user factory so it can be used under alias names.

factory :user, aliases: [:author, :commenter] do
  first_name { "John" }
  last_name { "Doe" }
  date_of_birth { 18.years.ago }

factory :post do
  # The alias allows us to write author instead of
  # association :author, factory: :user
  title { "How to read a book effectively" }
  body { "There are five steps involved." }

factory :comment do
  # The alias allows us to write commenter instead of
  # association :commenter, factory: :user
  body { "Great article!" }