In building Python 3.6.2 on Ubuntu 16.04, test_socket repeatedly fails at
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FAIL: testWithTimeoutTriggeredSend (test.test_socket.SendfileUsingSendfileTest)
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Traceback (most recent call last):
  File "/mnt/python/Python-3.6.2/Lib/test/test_socket.py", line 277, in _tearDown
    raise exc
  File "/mnt/python/Python-3.6.2/Lib/test/test_socket.py", line 295, in clientRun
    test_func()
  File "/mnt/python/Python-3.6.2/Lib/test/test_socket.py", line 5358, in _testWithTimeoutTriggeredSend
    self.assertRaises(socket.timeout, meth, file)
AssertionError: timeout not raised by _sendfile_use_sendfile

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It appears this is failing as _sendfile_use_sendfile completes before the 0.01s timeout set in _testWithTimeoutTriggeredSend

Adjusting FILESIZE in class SendfileUsingSendTest to 100MB instead of 10MB (or creating FILESIZE on class SendfileUsingSendfileTest so only that set of tests uses a 100MB file) succeeds.

issue17085 was a similar bug from a few years ago but I'm not sure that this can or should be solved in the same way...