def test_selectLast(self):
        """
        L{FDDetector._getImplementation} returns the last method from its
        C{_implementations} list if none of the implementations manage to return
        results which reflect a newly opened file descriptor.
        """
        def failWithWrongResults():
            return [3, 5, 9]

        def failWithOtherWrongResults():
            return [0, 1, 2]

        self.detector._implementations = [
            failWithWrongResults, failWithOtherWrongResults]

        self.assertIs(
            failWithOtherWrongResults, self.detector._getImplementation())

        L{FDDetector._getImplementation} returns the last method from its
        C{_implementations} list if none of the implementations manage to return
        results which reflect a newly opened file descriptor.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/internet/test/test_posixprocess.py