In 3.5 and up the asyncio test are pretty chatty with warnings. E.g. a recent run gave me this in 3.5:

./python.exe -m test.test_asyncio
.........................................................................................................../Users/guido/src/cpython/Lib/asyncio/selector_events.py:574: ResourceWarning: unclosed transport <_SelectorSslTransport closing fd=27>
  warnings.warn("unclosed transport %r" % self, ResourceWarning)
Task was destroyed but it is pending!
task: <Task pending coro=<BaseSelectorEventLoop._accept_connection2() done, defined at /Users/guido/src/cpython/Lib/asyncio/selector_events.py:192> wait_for=<Future pending cb=[Task._wakeup()]>>
.........................................................................Task was destroyed but it is pending!
task: <Task pending coro=<BaseSelectorEventLoop._accept_connection2() running at /Users/guido/src/cpython/Lib/asyncio/selector_events.py:227> wait_for=<Future finished exception=RuntimeError('Event loop is closed',)>>
/Users/guido/src/cpython/Lib/asyncio/selector_events.py:574: ResourceWarning: unclosed transport <_SelectorSocketTransport closing fd=26>
  warnings.warn("unclosed transport %r" % self, ResourceWarning)
...............................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................returning true from eof_received() has no effect when using ssl
...returning true from eof_received() has no effect when using ssl
...................................................................................................................................................................................................................................................................ss
----------------------------------------------------------------------
Ran 939 tests in 25.032s

OK (skipped=2)