OSIS-3949 add unit test on BusinessValidator._reset_messages()
OSIS-3949 add unit test on BusinessValidator._reset_messages()

uclouvain/OSIS-Louvain,uclouvain/OSIS-Louvain,uclouvain/osis,uclouvain/osis,uclouvain/OSIS-Louvain,uclouvain/osis,uclouvain/osis