Recent failure on AMD64 Windows7 SP1 3.8:
https://buildbot.python.org/all/#/builders/208/builds/268

test_huge_content_recvinto (test.test_asyncio.test_sock_lowlevel.ProactorEventLoopTests) ... C:\buildbot.python.org\3.8.kloth-win64\build\lib\test\support\__init__.py:1637: ResourceWarning: unclosed <socket.socket fd=564, family=AddressFamily.AF_INET, type=SocketKind.SOCK_STREAM, proto=0, laddr=('127.0.0.1', 59291), raddr=('127.0.0.1', 59290)>
ResourceWarning: Enable tracemalloc to get the object allocation traceback

ERROR: test_huge_content (test.test_asyncio.test_sock_lowlevel.ProactorEventLoopTests)

Re-running failed tests in verbose mode
C:\buildbot.python.org\3.8.kloth-win64\build\lib\test\support\__init__.py:1637: ResourceWarning: unclosed <socket.socket fd=456, family=AddressFamily.AF_INET, type=SocketKind.SOCK_STREAM, proto=0, laddr=('127.0.0.1', 3999), raddr=('127.0.0.1', 3998)>
ResourceWarning: Enable tracemalloc to get the object allocation traceback
FAIL: test_huge_content_recvinto (test.test_asyncio.test_sock_lowlevel.SelectEventLoopTests)