Classes with a lot of lines of code are generally bad. Too many responsibilities, low cohesion, or both. However, sometimes it is not possible to make functions smaller. Reasons could be various. What can be done in this circumstance?

Learn how to send a test email from a Laravel app

PHP 8.1 introduced the new Fiber class (see the proposed RFC here https://wiki.php.net/rfc/fiber), which allows running coroutines inside your script, i.e. two functions executing simultaneously

This article describes a TDD (Test Driven Development) approach to implement a Finite State Machine (FSM) using PHP+Laravel. However, such method is general and could be used in the programming language of your choice.