def test_removeAll(self):
        """
        Calling C{removeAll} on a reactor includes descriptors that are
        filesystem files.
        """
        reactor = self.buildReactor()
        self.addCleanup(self.unbuildReactor, reactor)

        path = self.mktemp()
        open(path, "wb").close()

        # Cleanup might fail if file is GCed too soon:
        self.f = f = open(path, "rb")

        # Have the reader added:
        stdio = StandardIO(Protocol(), stdin=f.fileno(),
                           stdout=self.extraFile.fileno(), reactor=reactor)
        # And then removed:
        removed = reactor.removeAll()
        self.assertIn(stdio._reader, removed)
        self.assertNotIn(stdio._reader, reactor.getReaders())

        Calling C{removeAll} on a reactor includes descriptors that are
        filesystem files.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/internet/test/test_stdio.py