======================================================================
FAIL: test_imap4_host_default_value (test.test_imaplib.TestImaplib)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/home/python/Lib/test/test_imaplib.py", line 94, in test_imap4_host_default_value
    self.assertIn(cm.exception.errno, expected_errnos)
AssertionError: 101 not found in [111, 99]

----------------------------------------------------------------------

I guess `errno.ENETUNREACH` should be added to the `expected_errnos` as it done within `test_create_connection` (test.test_socket.NetworkConnectionNoServer).

Did you see this failure somewhere in CI or is it in local machine? The imaplib test has below comment : 

if hasattr(errno, 'EADDRNOTAVAIL'):
    # socket.create_connection() fails randomly with
    # EADDRNOTAVAIL on Travis CI.
    expected_errnos.append(errno.EADDRNOTAVAIL)

As noted in initial report test_socket has ENETUNREACH added https://github.com/python/cpython/blob/929b70473829f04dedb8e802abcbd506926886e1/Lib/test/test_socket.py#L4808 so ENETUNREACH could also be added to this test too?

I see this error on my local Bamboo CI (runs on CentOS 7).

New changeset 3c7931e514faf509a39c218c2c9f55efb434628f by Victor Stinner in branch 'master':
bpo-36629: Add support.get_socket_conn_refused_errs() (GH-12834)
https://github.com/python/cpython/commit/3c7931e514faf509a39c218c2c9f55efb434628f

New changeset 28ed39e83e4c545fa1da89fd7691cace280296f7 by Victor Stinner (Miss Islington (bot)) in branch '3.7':
bpo-36629: Add support.get_socket_conn_refused_errs() (GH-12834) (GH-12835)
https://github.com/python/cpython/commit/28ed39e83e4c545fa1da89fd7691cace280296f7

Thanks for your bug report Marat Sharafutdinov, it's now fixed in 3.7 and master (Python 2.7 is not affected, it doesn't have the test_imaplib test method).

Thank you for the patch, Victor!