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ERROR: Stress test multiple threads and processes.
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Traceback (most recent call last):
  File "/home/travis/virtualenv/pypy-2.5.0/site-packages/nose/case.py", line 197, in runTest
    self.test(*self.arg)
  File "/home/travis/build/grantjenks/python-diskcache/tests/stress_test_fanout.py", line 280, in stress_test_mp
    stress_test()
  File "/home/travis/build/grantjenks/python-diskcache/tests/stress_test_fanout.py", line 244, in stress_test
    cache.check()
  File "/home/travis/build/grantjenks/python-diskcache/diskcache/fanout.py", line 135, in check
    return sum((shard.check(fix=fix) for shard in self._shards), [])
  File "/home/travis/build/grantjenks/python-diskcache/diskcache/fanout.py", line 135, in <genexpr>
    return sum((shard.check(fix=fix) for shard in self._shards), [])
  File "/home/travis/build/grantjenks/python-diskcache/diskcache/core.py", line 873, in check
    warnings.warn('file not found: %s' % full_path)
UserWarning: file not found: tmp/000/90/06/d93b748a5ebea1fee3fc3fe441bf.val