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ERROR: test_copyxattr_symlinks (test.test_shutil.TestShutil)
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Traceback (most recent call last):
  File "/opt/Python-3.6.0/Lib/test/test_shutil.py", line 505, in test_copyxattr_symlinks
    os.setxattr(src, 'trusted.foo', b'42')
PermissionError: [Errno 1] Operation not permitted: '/tmp/tmpvlu10qdm/foo'

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The problem is that "trusted" attributes (in this case trusted.foo) are visible and accessible only to processes that have the CAP_SYS_ADMIN capability. The current "skipUnless" guard is wrong: being root (UID 0) doesn't necessarely imply you have CAP_SYS_ADMIN. For instance this test (and thus "make test") will always fail in a Docker container unless it's started with "--cap-add SYS_ADMIN" (which, in general, is not the best thing to do).