Nearly a third of the harness is documented using the company standard in [yardoc](http://yardoc.org/). There's also a [guide to contributing documentation to the harness](https://github.com/puppetlabs/beaker/blob/master/DOCUMENTING.md) and [rake tasks to help](https://github.com/puppetlabs/beaker/blob/master/Rakefile#L52-L120).