Major Description
TestServers failed when running whole test. Because TestServers uses ServerStats instance directly. ServerStats is a static instance, which will be used across whole testing. so the numSuccessOps would not be zero, the assertion would fail.
Same problem occurs in TestBKStats. TestBKStats doesn't fail because statistics is turned off by default. The value happened to be zero. But it still is not a good idea to use static instance during testing.