Improve readability of graph testcases

[wmdi]

Eventually it would be good to add infrastructure to include dot descriptions of these graphs in these testcases for readability accompanied with checks to make sure they don't get out of date. It might even be worth writing a quick parser and DSL for specifying them as otherwise it's hard to tell what these testcases are actually doing (at least for people who didn't write the testcases themselves 🙂 )