'L{FDDetector._getImplementation} returns the first method from its
C{_implementations} list which returns results which reflect a newly
opened file descriptor.'

def test_selectFirstWorking(self):

    def failWithException():
        raise ValueError('This    does    not    work')
    def failWithWrongResults():
        return [0, 1, 2]
    def correct():
        return self._files[:]
    self.detector._implementations = [failWithException, failWithWrongResults, correct]
    self.assertIs(correct, self.detector._getImplementation())
