def _catc_tags(start_num, end_num):
    """
    Return a list of CATC tags corresponding to the start test number and end
    test number.  For example, start=1 and end=3 would return:
    ["CATC-001", "CATC-002", "CATC-003"].
    """
    return ["CATC-0{0:02d}".format(i) for i in range(start_num, end_num + 1)]