I rather like what go has set up for test's. They made it as small and functional as they could. Out of curiosity. How does a language specifically support "ag

I rather like what go has set up for test's. They made it as small and functional as they could. Out of curiosity. How does a language specifically support "agile refactoring"? What features permit (or hinder) stopping every couple of weeks and removing the accumulated WTF's in the codebade? Want to buy a left handed stapler?