Thanks for the recommendation Wasabi375! I was not aware of that plugin. I will look into it in more detail when I have time, but if it’s too much work to set up only for testing (without affecting the development compilation) then I probably won’t use it.
For the moment what I did is set the protected methods I need to unit test as internal and added a TODO so I can make them protected once I find a better solution. It’d be great to get some official support for this, maybe a plugin like the one you mentioned but that changes the visibility of methods or classes only for testing.