I actually only added lighthouse recently, it is a very minor part of the tests. Everything besides the 'performance' and 'vulnerabilities' tab are custom built 100%. These are:

* The layout tests and fullscreen rendering engine

* Spelling tests and highlighting

* Broken links check

* Structure visualization

* Error/console logs

* Broke resources / images

Lighthouse does have some nice SEO related information that I'm planning to expose in an easier way.