There are libraries that have different “adapters” for use in production, development, and test environments. This is sort of similar to dependency injection.
Take the Swoosh hex library for sending emails. You set the adapter (a module that follows a behaviour) in configuration. In production, you choose an adapter corresponding to your email service — say, the SendGrid adapter. In test, you use the Test adapter which is wired up to allow you to perform assertions on whether an email was sent and if it contained the right data. In development, you use a special adapter that captures “sent emails” in memory in a process, so that you can go to a special local route and view what would have been sent were it production.
