I told in the discussions forum for mr. Douglas that may be in this case factory pattern is excess. And I just send pull request. Because I really think that it is more clearly and elegant solution than to have several static variables contains Runnable implementation.
What will you do if you will need to add more 10 test runnable implementations? You will add more 10 static variables. I think more flexible to store all implementation in one special place. And it will be easy to extract this class in own class file if it will be huge. It's about benefit.

About 1st point. Consider you want to add new test in realization with static vars. You still need to add new static var. Do you think it is really easier than add new enum item?