kqueue doesn't support character devices like PTY before Mac OS 10.9. This issue is discussion on Tulip mailing list, no decision was taken yet how to fix this issue.

http://buildbot.python.org/all/builders/AMD64%20Snow%20Leop%203.x/builds/1071/steps/test/logs/stdio

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ERROR: test_read_pty_output (test.test_asyncio.test_events.KqueueEventLoopTests)
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Traceback (most recent call last):
  File "/Users/buildbot/buildarea/3.x.murray-snowleopard/build/Lib/asyncio/selector_events.py", line 135, in add_reader
    key = self._selector.get_key(fd)
  File "/Users/buildbot/buildarea/3.x.murray-snowleopard/build/Lib/selectors.py", line 181, in get_key
    raise KeyError("{!r} is not registered".format(fileobj)) from None
KeyError: '7 is not registered'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/Users/buildbot/buildarea/3.x.murray-snowleopard/build/Lib/test/test_asyncio/test_events.py", line 980, in test_read_pty_output
    self.loop.run_until_complete(connect())
  File "/Users/buildbot/buildarea/3.x.murray-snowleopard/build/Lib/asyncio/base_events.py", line 177, in run_until_complete
    return future.result()
  File "/Users/buildbot/buildarea/3.x.murray-snowleopard/build/Lib/asyncio/futures.py", line 236, in result
    raise self._exception
  File "/Users/buildbot/buildarea/3.x.murray-snowleopard/build/Lib/asyncio/tasks.py", line 281, in _step
    result = next(coro)
  File "/Users/buildbot/buildarea/3.x.murray-snowleopard/build/Lib/test/test_asyncio/test_events.py", line 974, in connect
    master_read_obj)
  File "/Users/buildbot/buildarea/3.x.murray-snowleopard/build/Lib/asyncio/base_events.py", line 537, in connect_read_pipe
    transport = self._make_read_pipe_transport(pipe, protocol, waiter)
  File "/Users/buildbot/buildarea/3.x.murray-snowleopard/build/Lib/asyncio/unix_events.py", line 149, in _make_read_pipe_transport
    return _UnixReadPipeTransport(self, pipe, protocol, waiter, extra)
  File "/Users/buildbot/buildarea/3.x.murray-snowleopard/build/Lib/asyncio/unix_events.py", line 200, in __init__
    self._loop.add_reader(self._fileno, self._read_ready)
  File "/Users/buildbot/buildarea/3.x.murray-snowleopard/build/Lib/asyncio/selector_events.py", line 138, in add_reader
    (handle, None))
  File "/Users/buildbot/buildarea/3.x.murray-snowleopard/build/Lib/selectors.py", line 462, in register
    self._kqueue.control([kev], 0, 0)
OSError: [Errno 22] Invalid argument

The issue was discussed here:
https://groups.google.com/d/msg/python-tulip/I8oJ65Ww2Zw/tVL2ppXiU54J

The decision is to skip the test on Mac OS X < 10.9.

New changeset 424564cffad0 by Victor Stinner in branch 'default':
Close #20365: Skip test_asyncio.test_events.test_read_pty_output() on Mac OS X
http://hg.python.org/cpython/rev/424564cffad0