According to this buildbot:

https://buildbot.python.org/all/#/builders/170/builds/218/steps/4/logs/stdio

there is some cleanup failure in test_sock_sendfile_os_error_first_call:

test_sock_sendfile_os_error_first_call (test.test_asyncio.test_unix_events.SelectorEventLoopUnixSockSendfileTests) ... /usr/home/buildbot/python/3.7.koobs-freebsd10.nondebug/build/Lib/asyncio/selector_events.py:655: ResourceWarning: unclosed transport <_SelectorSocketTransport fd=10>
  source=self)
ResourceWarning: Enable tracemalloc to get the object allocation traceback
ok

The code that is supposed to clean up the resource is:

        def cleanup():
            if proto.transport is not None:
                # can be None if the task was cancelled before
                # connection_made callback
                proto.transport.close()
                self.run_loop(proto.wait_closed())

apparently, proto.transport may be None and then it fails to be closed even if the test succeeds (I assume because the condition in the comment happens or something else) and then the transport is not properly closed.

New changeset d51324a2f5d172665f8824b25456c9822797fc84 by Pablo Galindo in branch 'master':
bpo-35602: Make sure the transport is always closed in SelectorEventLoopUnixSockSendfileTests (GH-11338)
https://github.com/python/cpython/commit/d51324a2f5d172665f8824b25456c9822797fc84

New changeset fe06646d186780881fa5ee61442886a6d7cf9f08 by Miss Islington (bot) in branch '3.7':
bpo-35602: Make sure the transport is always closed in SelectorEventLoopUnixSockSendfileTests (GH-11338)
https://github.com/python/cpython/commit/fe06646d186780881fa5ee61442886a6d7cf9f08