$ ./python -bWerror -m test -r -u all
. . .
0:12:58 [ 70/402] test_asyncio
Exception ignored in: <bound method _SSLProtocolTransport.__del__ of <asyncio.sslproto._SSLProtocolTransport object at 0x7fed4638f0c0>>
Traceback (most recent call last):
  File "/media/disk/home/proj/python/cpython/Lib/asyncio/sslproto.py", line 329, in __del__
    source=self)
ResourceWarning: unclosed transport <asyncio.sslproto._SSLProtocolTransport object at 0x7fed4638f0c0>
Exception ignored in: <bound method _SSLProtocolTransport.__del__ of <asyncio.sslproto._SSLProtocolTransport object at 0x7fed46317c88>>
Traceback (most recent call last):
  File "/media/disk/home/proj/python/cpython/Lib/asyncio/sslproto.py", line 329, in __del__
    source=self)
ResourceWarning: unclosed transport <asyncio.sslproto._SSLProtocolTransport object at 0x7fed46317c88>
Exception ignored in: <bound method _SSLProtocolTransport.__del__ of <asyncio.sslproto._SSLProtocolTransport object at 0x7fed46310f60>>
Traceback (most recent call last):
  File "/media/disk/home/proj/python/cpython/Lib/asyncio/sslproto.py", line 329, in __del__
    source=self)
ResourceWarning: unclosed transport <asyncio.sslproto._SSLProtocolTransport object at 0x7fed46310f60>
Executing <Task finished coro=<CoroutineTests.test_async_def_wrapped.<locals>.start() done, defined at /media/disk/home/proj/python/cpython/Lib/test/test_asyncio/test_pep492.py:149> result=None created at /media/disk/home/proj/python/cpython/Lib/asyncio/base_events.py:367> took 0.351 seconds

If necessary, you should be able to run with python -Wall -X tracemalloc=33 to get a stack dump where the resources (transport objects or whatever) were allocated.