Suggestion: Add documentation for unit test infrastructure

[AnthonyMDev]

When I make PRs for ReactiveKit, I've tried to add unit tests, but I've been having a difficult time.

There is a lot of interesting test helper utilities you've created to make your unit tests easier to write, but it's difficult to understand what it's doing or how to use it.
Writing some documentation and maybe a simple usage guide would be really helpful.

I know this is a pretty low priority issue, but it's definitely something that's been a pain point for me. I've tried digging into it a little bit, but still haven't been able to really figure out how to write tests for ReactiveKit.

Note: This isn't about writing unit tests for my personal code that uses ReactiveKit, this is about writing tests for the actual ReactiveKit code base when I make PRs for this library. (Same goes for Bond)