since this CL landed, this test has failed on my box:
https://chromium-review.googlesource.com/352241

it's because i have a symlink at ~/chromiumos/ and this test apparently doesn't like that.
$ ls -l ~/chromiumos
lrwxrwxrwx 1 vapier eng 25 May 30  2012 /usr/local/google/home/vapier/chromiumos -> /usr/local/src/chromiumos

if i go to ~/chromiumos/chromite/, the test fails.  if i go to /usr/local/src/chromiumos/chromite/, the test passes.

$ git checkout b24070c2424a849e31067eed81d422d1fd5f8c4d^
$ cbuildbot/stages/sync_stages_unittest SyncStageRepoCacheTest.testInitializeRepoNotPopulatedCache
18:23:56: INFO: Using warm cache "/tmp/chromite.tests36fxu/cache" to populate buildroot "/tmp/chromite.tests36fxu/buildroot"
.
----------------------------------------------------------------------
Ran 1 test in 0.521s

OK

$ git checkout b24070c2424a849e31067eed81d422d1fd5f8c4d
$ cbuildbot/stages/sync_stages_unittest SyncStageRepoCacheTest.testInitializeRepoNotPopulatedCache 
18:23:26: INFO: Using warm cache "/tmp/chromite.testLva2za/cache" to populate buildroot "/tmp/chromite.testLva2za/buildroot"
F
======================================================================
FAIL: [chromite.cbuildbot.stages.sync_stages_unittest] SyncStageRepoCacheTest.testInitializeRepoNotPopulatedCache
Tests basic SyncStage repo cache initialization code.
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/usr/local/src/chromiumos/chromite/lib/timeout_util.py", line 171, in TimeoutWrapper
    func(*args, **kwargs)
  File "/usr/local/src/chromiumos/chromite/cbuildbot/stages/sync_stages_unittest.py", line 226, in testInitializeRepoNotPopulatedCache
    self.validateCache()
  File "/usr/local/src/chromiumos/chromite/cbuildbot/stages/sync_stages_unittest.py", line 195, in validateCache
    self.assertFalse(os.path.exists(broken))
AssertionError: True is not false