'The str of a L{FirstError} instance includes the str of the
sub-failure and the index which corresponds to the L{FirstError}.'

def test_str(self):

    exc = ValueError('some    text')
    try:
        raise exc
    except:
        f = failure.Failure()
    error = defer.FirstError(f, 5)
    self.assertEqual(str(error), ('FirstError[#5,    %s]' % (str(f),)))
