Related failure:

https://buildbot.python.org/all/#/builders/141/builds/1233


----------------------------------------------------------------------
Ran 56 tests in 25.105s
OK (skipped=1)
Re-running test 'test_normalization' in verbose mode
test_bug_834676 (test.test_normalization.NormalizationTest) ... ok
test test_normalization failed
test_main (test.test_normalization.NormalizationTest) ... 	fetching http://www.pythontest.net/unicode/11.0.0/NormalizationTest.txt ...
FAIL
======================================================================
FAIL: test_main (test.test_normalization.NormalizationTest)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/srv/buildbot/buildarea/3.x.bolen-ubuntu/build/Lib/urllib/request.py", line 1316, in do_open
    h.request(req.get_method(), req.selector, req.data, headers,
socket.gaierror: [Errno -3] Temporary failure in name resolution
During handling of the above exception, another exception occurred:
Traceback (most recent call last):
  File "/srv/buildbot/buildarea/3.x.bolen-ubuntu/build/Lib/test/test_normalization.py", line 41, in test_main
    testdata = open_urlresource(TESTDATAURL, encoding="utf-8",
urllib.error.URLError: <urlopen error [Errno -3] Temporary failure in name resolution>
During handling of the above exception, another exception occurred:
Traceback (most recent call last):
  File "/srv/buildbot/buildarea/3.x.bolen-ubuntu/build/Lib/test/test_normalization.py", line 47, in test_main
    self.fail(f"Could not retrieve {TESTDATAURL}")
AssertionError: Could not retrieve http://www.pythontest.net/unicode/11.0.0/NormalizationTest.txt
----------------------------------------------------------------------
Ran 2 tests in 20.044s
FAILED (failures=1)
Re-running test 'test_urllib2net' in verbose mode
test_close (test.test_urllib2net.CloseSocketTest) ... skipped "Resource 'http://www.example.com/' is not available"
test_custom_headers (test.test_urllib2net.OtherNetworkTests) ... skipped "Resource 'http://www.example.com' is not available"
test_file (test.test_urllib2net.OtherNetworkTests) ... ok
test_ftp (test.test_urllib2net.OtherNetworkTests) ... ok
test_redirect_url_withfrag (test.test_urllib2net.OtherNetworkTests) ... skipped "Resource 'http://www.pythontest.net/redir/with_frag/' is not available"
test_sites_no_connection_close (test.test_urllib2net.OtherNetworkTests) ... skipped 'XXX: http://www.imdb.com is gone'
test_urlwithfrag (test.test_urllib2net.OtherNetworkTests) ... skipped "Resource 'http://www.pythontest.net/index.html#frag' is not available"
test_ftp_basic (test.test_urllib2net.TimeoutTest) ... ok
test_ftp_default_timeout (test.test_urllib2net.TimeoutTest) ... ok
test_ftp_no_timeout (test.test_urllib2net.TimeoutTest) ... ok
test_ftp_timeout (test.test_urllib2net.TimeoutTest) ... ok
test_http_basic (test.test_urllib2net.TimeoutTest) ... ok
test_http_default_timeout (test.test_urllib2net.TimeoutTest) ... ok
test_http_no_timeout (test.test_urllib2net.TimeoutTest) ... ok
/srv/buildbot/buildarea/3.x.bolen-ubuntu/build/Lib/test/support/__init__.py:1608: ResourceWarning: unclosed <socket.socket fd=3, family=AddressFamily.AF_INET, type=SocketKind.SOCK_STREAM, proto=6, laddr=('45.56.109.169', 46650), raddr=('104.236.16.9', 21)>
  gc.collect()
ResourceWarning: Enable tracemalloc to get the object allocation traceback
/srv/buildbot/buildarea/3.x.bolen-ubuntu/build/Lib/test/support/__init__.py:1608: ResourceWarning: unclosed <socket.socket fd=4, family=AddressFamily.AF_INET, type=SocketKind.SOCK_STREAM, proto=6, laddr=('45.56.109.169', 46662), raddr=('104.236.16.9', 21)>
  gc.collect()
ResourceWarning: Enable tracemalloc to get the object allocation traceback
test_http_timeout (test.test_urllib2net.TimeoutTest) ... ok
----------------------------------------------------------------------
Ran 15 tests in 686.335s
OK (skipped=5)
1 test failed again:
    test_normalization

Also, it seems that there are some socket leaks.