I'm always happy to hear when people write new adapters for karma :)
There is no template at the moment but I suggest looking at karma-mocha and karma-jasmine for inspiration/details. In general it sounds good to use the pubsub system from preamble to gather the needed data if all you need is exposed there I can't say much more on that though as I don't know how preamble works internally.
Good luck and let us know if you need more help.
Cheers
Friedel