hegel | An advanced static type checker | Runtime Evironment library

__init_subclass__ and __set_name__ are orthogonal mechanisms - they're not tied to each other, just described in the same PEP. Both are features that needed a full-featured metaclass before. The PEP 487 addresses 2 of the most common uses of metaclasses:

• how to let the parent know when it is being subclassed (__init_subclass__)
• how to let a descriptor class know the name of the property it is used for (__set_name__)

As the PEP says:

While there are many possible ways to use a metaclass, the vast majority of use cases falls into just three categories: some initialization code running after class creation, the initialization of descriptors and keeping the order in which class attributes were defined.

The first two categories can easily be achieved by having simple hooks into the class creation:

• An __init_subclass__ hook that initializes all subclasses of a given class.
• upon class creation, a __set_name__ hook is called on all the attribute (descriptors) defined in the class, and

The third category is the topic of another PEP, PEP 520.

Notice also, that while __init_subclass__ is a replacement for using a metaclass in this class's inheritance tree, __set_name__ in a descriptor class is a replacement for using a metaclass for the class that has an instance of the descriptor as an attribute.

I would favor the simplified unit test. If you decide to change the functionality of this code, it'll be much easier to update the simplified unit test rather than the long and complex one.

Aside from that, the purpose of unit tests is to check whether small components of code work at their base level for realistic expected inputs, reduced to the smallest amount of complexity. If you find that the unit test to check the base functionality is too complex, you may want to split up the function into smaller components in itself. In this case, I think your functionality is straightforward enough and you would benefit more from the simple unit test than the complex one. However, this question is definitely opinion-based.