The test_listdir test from Lib/test/test_os.py is using os.listdir() twice in the root directory with and without parameters and compares the results. I just had the test fail for me, because an unrelated process happened to create a file in the root directory between the two invocations of os.listdir. In my case it was rsyslog creating '/imjournal.state.tmp', but the problem is a general one.

The test failed with:
```
   ..test test_os failed -- Traceback (most recent call last):
  File "/home/matthiasb/dev/fbcpython/Lib/test/test_os.py", line 1914, in test_listdir
    self.assertEqual(set(os.listdir()), set(os.listdir(os.sep)))
AssertionError: Items in the first set but not the second:
'imjournal.state.tmp'
```