Sorry for the use of pictures here but it seemed appropriate.
I have a simple method interceptor working in the first image, but when I move my interceptor to be a part of the library that I want it to live in (for reusability) it just stops weaving.
Adding [module: Interceptor] to the FodyTest project was the solution to the issue.
A change since fody version 3 makes this necessary in the newer fody.
Thanks for the tip Lucas Trzesniewski