Codeigniter 4 extend core class process clarification

Testing Session is difficult. Because Session does not work in CLI.
So if you are not an expert, I recommend you test via web.

CI4 provides MockSession for PHPUnit testing.
So if you replace Session, you need to create your MockSession,
and a feature to use your MockSession in your test case.
See https://github.com/codeigniter4/CodeIgni...#L332-L343

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