NodeNES is aimed to be a full NES ide in the Browser. It have a c6502 compiler compatible with NESASM and a Sprite Editor. It was build using TDD as a filosophy and not just a way of codding.
Tests are great and really guide this project. Every step was followed by a test. The compiler have grown around tests. Therefore its compability has incresed along with demos and examples provided as fixtures. You can even track the learning proccess watching the commit log over the history of the project. You will find several ways to steal on tests before the end of the race.
Just use the run task
I will try to put a list of current issues on the Github Issues. If you don't know where to start, ask-me. I will sure find something easy to start.