best way to debug CI

Try using <?PHP STRICT_TYPES=1); at the start of every PHP file (it is not hereditary and only applies to that file). This ensures warnings are not “swept under the carpet”, errors are raised instead and require fixing before proceeding.

Also set error_reporting(-1):, which is maximum errors.

Only disable ini_set(‘display_errors’, ‘false’); on production to ensure both errors and warnings are logged.

I use phpStorm and xdebug and they work great together. I am debugging in a docker container too, just to make it a little more complex .  A few years ago someone up on this forum recommended phpStorm, and I'd say it was one of the best decisions I have ever made. I am an IDE centric guy from way back.

Yeah, PhpStorm is very good!

ci-phpunit-test | CodeIgniter Testing Guide | CodeIgniter 3 to 4 Upgrade Helper

I am a newbie learning PHP and also using firephp extension it is really awesome and helping me a lot in my university project.