Docuemnt access to Dependency injection for Tests

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• I have checked for existing issues and pull requests related to my suggestion.
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Type of Suggestion

Proposing new documentation content

Relevant Documentation Links

https://docs.nextcloud.com/server/latest/developer_manual/basics/testing.html#php

Summary

Explicitly state how to realize dependency injection for unit and integration tests

Details

The DI framework in NC is nice and works out of the box without manual configuration by the app devs. However, when testing classes using PHPUnit, the DI framework is not available. That is okay for simple unit tests that only rely on a few classes that can be mocked/stubbed.
However, once integration tests should be carried out or larger class structures should be addresses, the DI is very handy. In the example, there is a way presented to get the app container from the application class. I would like to see this more verbose and more present.

Additional Notes

I might write this myself. Here just to keep track...

Start with the PHP section of the linked developer testing documentation and review its existing application-container example. Expand the guidance to explain dependency injection for PHPUnit unit and integration tests, with enough detail for larger class structures; done means the workflow is explicit and usable without relying on unstated project knowledge.