Any tutorials on Unit testing in CI4?

I would like to do some testing before deploying the app updates to the server, some CLI script that would run my controllers with the standard data and make sure there are no critical errors, so users do not see the "oops..." page quite so often I imagine I need to write unit tests for that.
I have never done unit testing and the content in Codeigniter 4 documentation seems to be written for those who know what it is pretty well and only need some hints on doing it the CI4 way.
Could someone point me in the right direction? Easiest would be to find some simple tutorial about unit-testing controllers in CI, but in case there are none - how would you proceed to make learning PHP unit testing and writing tests the CI4 way as painless and short as possible?

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Donatas G.