PL/Unit is a unit test framework for Oracle 8i and above. 
 
It is very lightweight, there is only one package installed, no other objects are created.  It is integrated with Apollo Pro, an Oracle development tool.  You can download it here: http://www.apollopro.com

Also, there is a tutorial available online that shows you how to use PL/Unit to solve a simple problem. http://www.apollopro.com/help/tdd_tutorial_1.htm.

You can read more about PL/Unit here: http://www.apollopro.com/help/pl_unit.htm