Crap - Ok, I hadn't clued in to the cache resizing issue on concurrent-write on get(). these tests do test the basic double-check.  I didn't write them to catch a regression, I wrote them to prove that I had written the double-check correctly. 

Talking to louis, and a few others, I think I need to use different collections here, and the prime candidates are buried in MapMaker and CacheBuilder in Guava.  I may need to rip them out, so I can get weak keys and concurrent write safety for get().