This issue now prevents me to merge https://github.com/python/cpython/pull/26414 backport :-(

I'm debugging it on Windows.

I tried:

vstinner@DESKTOP-DK7VBIL C:\vstinner\python\main>python -u -X dev -m test -u all test_ssl -m test_pha_required_nocert -v -F -j2
(...)
0:00:35 load avg: 8.32 [ 77/1] test_ssl failed
test_ssl: testing with 'OpenSSL 1.1.1k  25 Mar 2021' (1, 1, 1, 11, 15)
          under Windows ('10', '10.0.19042', 'SP0', 'Multiprocessor Free')
          HAS_SNI = True
          OP_ALL = 0x-7fffffac
          OP_NO_TLSv1_1 = 0x10000000
test_pha_required_nocert (test.test_ssl.TestPostHandshakeAuth) ...  server:  new connection from ('127.0.0.1', 51115)
 client cert is None
 client did not provide a cert
 server: connection cipher is now ('TLS_AES_256_GCM_SHA384', 'TLSv1.3', 256)
TLS: (<ssl.SSLSocket fd=680, family=AF_INET, type=SOCK_STREAM, proto=0, laddr=('127.0.0.1', 51114), raddr=('127.0.0.1', 51115)>, 'write', TLSVersion.TLS
v1_3, _TLSContentType.ALERT, _TLSAlertType.CERTIFICATE_REQUIRED, b'\x02t')
Test server failure:
Traceback (most recent call last):
   File "C:\vstinner\python\main\lib\test\test_ssl.py", line 2444, in run
    msg = self.read()
   File "C:\vstinner\python\main\lib\test\test_ssl.py", line 2421, in read
    return self.sslconn.read()
   File "C:\vstinner\python\main\lib\ssl.py", line 1131, in read
    return self._sslobj.read(len)
 ssl.SSLError: [SSL: PEER_DID_NOT_RETURN_A_CERTIFICATE] peer did not return a certificate (_ssl.c:2523)
FAIL

======================================================================
FAIL: test_pha_required_nocert (test.test_ssl.TestPostHandshakeAuth)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "C:\vstinner\python\main\lib\test\test_ssl.py", line 4458, in test_pha_required_nocert
    with self.assertRaisesRegex(
AssertionError: SSLError not raised


This is not the crash, but the fact that the test is not reliable doesn't help to debug :-(


Moreover, I had to patch unittest locally, since a frame globals was None!?

test test_ssl crashed -- Traceback (most recent call last):
  File "C:\vstinner\python\main\lib\test\libregrtest\runtest.py", line 282, in _runtest_inner
    refleak = _runtest_inner2(ns, test_name)
  (...)
  File "C:\vstinner\python\main\lib\unittest\result.py", line 209, in _count_relevant_tb_levels
    while tb and not self._is_relevant_tb_level(tb):
  File "C:\vstinner\python\main\lib\unittest\result.py", line 205, in _is_relevant_tb_level
    return '__unittest' in tb.tb_frame.f_globals
TypeError: argument of type 'NoneType' is not iterable