I'm currently developing a business framework for my start-up company and I was already in the process of creating similar testing library to test my framework to ease the pain but then I stumbled upon this library while researching and I was really glad that it's done.
So I started to use this library but I didn't really want to change my existing tests drastically so I created some extensions and it's all working but because this library already has so many extension methods available it causes some noise in the intellisense so I thought that it might be a good idea to move features and non-core methods to another assembly to let developers the ability to use a different style of testing if they wish and build upon this library infrastructures rather than creating their own.
Hopefully it make sense.