assertSequenceEqual() raises BytesWarning when format failure report. See for example http://buildbot.python.org/all/builders/AMD64%20OpenIndiana%203.x/builds/10575/steps/test/logs/stdio :

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ERROR: test_close_fds_0_1 (test.test_subprocess.POSIXProcessTestCase)
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Traceback (most recent call last):
  File "/export/home/buildbot/64bits/3.x.cea-indiana-amd64/build/Lib/test/test_subprocess.py", line 1741, in test_close_fds_0_1
    self.check_close_std_fds([0, 1])
  File "/export/home/buildbot/64bits/3.x.cea-indiana-amd64/build/Lib/test/test_subprocess.py", line 1727, in check_close_std_fds
    self.assertEqual((out, err), (b'apple', b'orange'))
  File "/export/home/buildbot/64bits/3.x.cea-indiana-amd64/build/Lib/unittest/case.py", line 820, in assertEqual
    assertion_func(first, second, msg=msg)
  File "/export/home/buildbot/64bits/3.x.cea-indiana-amd64/build/Lib/unittest/case.py", line 1029, in assertTupleEqual
    self.assertSequenceEqual(tuple1, tuple2, msg, seq_type=tuple)
  File "/export/home/buildbot/64bits/3.x.cea-indiana-amd64/build/Lib/unittest/case.py", line 967, in assertSequenceEqual
    (i, item1, item2))
BytesWarning: str() on a bytes instance

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Proposed patch fixes message formatting and adds tests for assertions that can emit BytesWarning.