Twigwas created as a new instance each time. It only took ~.03s, but this function is called on updates and in plugin manager when a plugin is activated/installed/deactivated/uninstalled. Which means it is run multiple times for each plugin every time a Fixture is setup, and since there are many integration tests this means it is run quite a lot.
In total seems to save > 8mins. Will eventually have to split the build between core & plugins, though.