(My initial messages contained a mistaken idea based on a mis-remembering the details sys.last values and exceptions.)

If an exception is not caught and a traceback is printed, sys.last_type, sys.last_value, and sys.last_traceback are set.  When an exception is caught, the last_ x values are not touched, but the same are available by calling sys.exc_info.  Stackview accessed all 3 sys.last_x values, but they are not normally set when testing because exception are caught.  The test sets them from a sys.exc_info after catching an exception.