When it will be possible to run testing environment?

You can't use `testing` for your development. It is the specification, not a bug.

> The environment testing is the special one for PHPUnit testing. It has special conditions built into the framework at various places to assist with that. You can’t use it for your development.
https://codeigniter4.github.io/CodeIgnit...t-constant

What's wrong with useing `development`?

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