def test_filter_ips_white_list(self):
        CONF.network_label_regex = '.*'
        CONF.ip_regex = '^(15.|123.)'
        CONF.black_list_regex = '^10.123.123.*'
        ip = self.instance.get_visible_ip_addresses()
        ip = filter_ips(
            ip, CONF.ip_regex, CONF.black_list_regex)
        self.assertEqual(2, len(ip))
        self.assertTrue('123.123.123.123' in ip)
        self.assertTrue('15.123.123.123' in ip)
def union(matches, root, cwd):
    """Union a list of matchers.

    If the list is empty, return nevermatcher.
    If the list only contains one non-None value, return that matcher.
    Otherwise return a union matcher.
    """
    matches = list(filter(None, matches))
    if len(matches) == 0:
        return nevermatcher(root, cwd)
    elif len(matches) == 1:
        return matches[0]
    else:
        return unionmatcher(matches)