Fix nasa#734, continue cleanup of SB unit test

Makes the SB unit test closer to recommended UT assert patterns

Do not keep a separate "TestStat" state variable outside UT assert.
Do not report separate status messages from the asserts.  Use UT assert.
Do not "reset" in the middle of a test routine, split into separate
test routines where this is done.
No need for "START" and "STARTBLOCK" or "ENDBLOCK".  UT assert has
messages for these test actions.  Each block should be a separate test
routine and then these are unnecessary.