Just want to suggest an alternative to mocha here. I'd really love if this could be considered as an option:

https://github.com/avajs/ava

Ava is a fantastic, modern framework that can run tests in parallel. It's ridiculously fast compared to mocha, It has support for modern JS features like async functions and it doesn't do any weird stuff like injecting globals into your tests. (Personally, this has always been a massive pain because editors and linters don't like it.).