'If C{inotify_add_watch} returns a negative number, L{add}
raises L{INotifyError}.'

def test_failedAddWatch(self):

    class libc:
        def inotify_add_watch(self, fd, path, mask):
            return (-1)
    self.patch(_inotify, 'libc', libc())
    self.assertRaises(INotifyError, add, 3, FilePath('/foo'), 0)
