Jest Run Config Source Follow

There's a feature I want to implement in my own Run Config plugin that looks like it would be similar to a feature that's in the Jest Run Config, but I'm not sure where to see the source code for the Jest Run Config. Is the plugin for Jest open source? If not, would it be possible to request the source? 

The feature that I'm interested in seeing the implementation of is highlighting the piece of code that causes a test to fail. When you run Jest tests and it fails, the expression that it fails on becomes highlighted. In my plugin (that's for mutation testing), I want to highlight the piece of source code that fails. I couldn't decide if Annotator or ExternalAnnotator (or maybe a CoverageEngine?) would be better, and I'd like to see how it's implemented for Jest tests