Provide details of where core tests, not in core modules, should live.

Problem/Motivation

Follow up from 📌 standardize docs on how to use the 4 types of test base RTBC

Steps to reproduce

N/A

Proposed resolution

TBD

Remaining tasks

File in summary

User interface changes

N/A

API changes

N/A

Data model changes

N/A

Release notes snippet

N/A