It would be good if for each bug-report, in mantis, a unit test is made, to avoid that if one bug is fixed we dint have broken another bug/test?
The regression testing of OCCT is based on Draw Harness application, which allows execution of OCCT-commands (extended by plugins) within tcl-scripts.
You can find scripts used for certification (automated regression-testing) in folder "tests". See chapter Automated Testing System in documentation for details.
You may find test scripts, associated with specific bug issue in field "Test case number" (for example: bugs vis(004) bug24902_1, bug24902_2).
OCCT is complex framework and complete database of Unit-tests would be quite huge, and technically functional tests are used instead (save the small exceptions).